Checkout: only customer fields on order updates, verified PayPal capture, safe logging (#6)

Co-authored-by: Michael Czechowski <mail@librete.ch>

config/logger.ts

@@ -1,10 +1,17 @@
 import { winston } from "@strapi/logger";
 import { formatLogLine } from "../src/logging/format";
 
+// Strapi 4.25 creates its logger from @strapi/logger's default configuration with this object assigned over it
+// (Strapi.js: createLogger(this.config.get("logger"))). Its default level is "silly", which writes every line, also the debug and
+// silly lines with order data such as names and addresses. Production (NODE_ENV=production in mp's compose.yml) writes info and
+// above, any other environment debug and above.
+const level = process.env.NODE_ENV === "production" ? "info" : "debug";
+
 export default {
+	level,
 	transports: [
 		new winston.transports.Console({
-			format: winston.format.combine(winston.format.printf(formatLogLine))
+			format: winston.format.combine(winston.format.printf((info) => formatLogLine(info, { stack: level === "debug" })))
 		})
 	]
 };

src/api/order/content-types/order/schema.json

@@ -83,6 +83,18 @@
     "paymentStatus": {
       "type": "string"
     },
+    "paypalOrderId": {
+      "type": "string",
+      "private": true
+    },
+    "paypalCaptureId": {
+      "type": "string",
+      "private": true
+    },
+    "paymentCapturedAt": {
+      "type": "datetime",
+      "private": true
+    },
     "emailSent": {
       "type": "boolean",
       "default": false

src/api/order/controllers/order.ts

@@ -1,9 +1,25 @@
 import { factories } from "@strapi/strapi";
 import { sanitize } from "@strapi/utils";
+import type { ID } from "@strapi/database/dist/types";
 import { Order } from "../../../../types";
 import { paypalApi } from "../../../services/PayPalApi";
 import { orderDefaultParams } from "../services/order";
 import { calculateTotalProductPrice } from "../../product/services/product";
+import { parseCustomerUpdate } from "../../../checkout/customer-update";
+import type { CustomerUpdate } from "../../../checkout/customer-update";
+import { isLockedForCustomer, missingCheckoutFields } from "../../../checkout/order-state";
+import { capturePayment } from "../../../checkout/capture-payment";
+import type { CaptureLog } from "../../../checkout/capture-payment";
+import { CHECKOUT_NOT_READY, checkoutFailure } from "../../../checkout/paypal-order";
+import { describeError } from "../../../logging/error";
+
+const ORDER_LOCKED = "Order can no longer be changed";
+
+const captureLog: CaptureLog = {
+	info: (message, fields) => strapi.log.info(`app:i:order-controller: ${message}`, fields),
+	warn: (message, fields) => strapi.log.warn(`app:w:order-controller: ${message}`, fields),
+	error: (message, fields) => strapi.log.error(`app:e:order-controller: ${message}`, fields)
+};
 
 /**
  * The order controller is a funnel for the client to interact with the order service.
@@ -68,6 +84,7 @@ export default factories.createCoreController("api::order.order", ({ strapi }) =
 			where: { id },
 			...orderDefaultParams
 		});
+		if (!order) return ctx.notFound("Order not found");
 		order.cart = order?.cart.map((item) => ({
 			...item,
 			product: {
@@ -75,7 +92,6 @@ export default factories.createCoreController("api::order.order", ({ strapi }) =
 				totalProductPrice: calculateTotalProductPrice(item.product)
 			}
 		}));
-		if (!order) return ctx.notFound("Order not found");
 		return await sanitize.contentAPI.output(order, strapi.getModel("api::order.order"));
 	},
 
@@ -85,6 +101,7 @@ export default factories.createCoreController("api::order.order", ({ strapi }) =
 			where: { uuid },
 			...orderDefaultParams
 		});
+		if (!order) return ctx.notFound("Order not found");
 		order.cart = order?.cart.map((item) => ({
 			...item,
 			product: {
@@ -92,35 +109,46 @@ export default factories.createCoreController("api::order.order", ({ strapi }) =
 				totalProductPrice: calculateTotalProductPrice(item.product)
 			}
 		}));
-		if (!order) return ctx.notFound("Order not found");
 		return await sanitize.contentAPI.output(order, strapi.getModel("api::order.order"));
 	},
 
+	/**
+	 * The customer's checkout steps: contact details, terms, addresses and delivery method. Only these fields are written;
+	 * payment state, totals, numbers and documents are written by the payment flow and the server alone.
+	 */
 	updateByUuid: async (ctx) => {
 		const { uuid } = await sanitize.contentAPI.query(ctx.params, strapi.getModel("api::order.order"));
 		const order = await strapi.db.query("api::order.order").findOne({ where: { uuid } });
 		if (!order) return ctx.notFound("Order not found");
+		if (isLockedForCustomer(order)) return ctx.conflict(ORDER_LOCKED);
 
-		const sanitizedBody = await sanitize.contentAPI.input(ctx.request.body, strapi.getModel("api::order.order"));
+		const update = parseCustomerUpdate(ctx.request.body, new Date());
+		if (update.ok === false) {
+			strapi.log.warn("app:w:order-controller: Rejected order update", { order: order.id, fields: update.fields });
+			return ctx.badRequest("Invalid order update", { errors: update.errors });
+		}
+		// A changed address or delivery method needs a new checkout: the PayPal order created before can no longer be captured.
+		const data: CustomerUpdate & { customer?: ID; paypalOrderId: null } = { ...update.data, paypalOrderId: null };
+
+		if (data.delivery !== undefined) {
+			const delivery = await strapi.db.query("api::delivery.delivery").findOne({ where: { id: data.delivery }, select: ["id"] });
+			if (!delivery) {
+				strapi.log.warn("app:w:order-controller: Rejected order update", { order: order.id, fields: ["data.delivery"] });
+				return ctx.badRequest("Invalid order update", { errors: ["data.delivery: no delivery method has this id"] });
+			}
+		}
 
 		// Handle customer creation/update if structured addresses are provided
-		// @ts-expect-error
-		if (sanitizedBody?.data?.invoiceAddressStructured) {
+		if (data.invoiceAddressStructured) {
+			const address = data.invoiceAddressStructured;
 			const customerAddress =
-				// @ts-expect-error
-				sanitizedBody.data.invoiceAddress ||
-				// @ts-expect-error
-				`${sanitizedBody.data.invoiceAddressStructured.givenName} ${sanitizedBody.data.invoiceAddressStructured.familyName}\n${sanitizedBody.data.invoiceAddressStructured.streetAddress}\n${sanitizedBody.data.invoiceAddressStructured.postalCode} ${sanitizedBody.data.invoiceAddressStructured.addressLevel2}`;
-			// @ts-expect-error
-			sanitizedBody.data.customer = await strapi
-				.service("api::customer.customer")
-				// @ts-expect-error
-				.findOrCreateCustomer(customerAddress, sanitizedBody.data.invoiceAddressStructured);
+				data.invoiceAddress ||
+				`${address.givenName} ${address.familyName}\n${address.streetAddress}\n${address.postalCode} ${address.addressLevel2}`;
+			data.customer = await strapi.service("api::customer.customer").findOrCreateCustomer(customerAddress, address);
 		}
 
 		const orderUnsafe = await strapi.service("api::order.order").update(order.id, {
-			// @ts-expect-error
-			data: sanitizedBody?.data,
+			data,
 			...orderDefaultParams
 		});
 
@@ -131,6 +159,7 @@ export default factories.createCoreController("api::order.order", ({ strapi }) =
 		const { uuid, productId } = await sanitize.contentAPI.query(ctx.params, strapi.getModel("api::order.order"));
 		const order = (await strapi.service("api::order.order").findOneByUuid(uuid)) as Order;
 		if (!order) return ctx.notFound("Order not found");
+		if (isLockedForCustomer(order)) return ctx.conflict(ORDER_LOCKED);
 
 		const product = parseInt(productId as string);
 		const count = parseInt(ctx.query.count as string) || 1;
@@ -147,8 +176,9 @@ export default factories.createCoreController("api::order.order", ({ strapi }) =
 
 		strapi.log.info(`app:v:order-controller: - Adding product to cart ${order.id}`, { totalBefore: order.total });
 
+		// A changed cart needs a new checkout: the PayPal order created before can no longer be captured.
 		const orderUnsafe = await strapi.service("api::order.order").update(order.id, {
-			data: { cart: cart },
+			data: { cart: cart, paypalOrderId: null },
 			...orderDefaultParams
 		});
 		strapi.log.info("app:v:order-controller: ✔ Adding product to cart", { totalAfter: orderUnsafe.total });
@@ -162,6 +192,7 @@ export default factories.createCoreController("api::order.order", ({ strapi }) =
 		const product = parseInt(productId as string);
 
 		if (!order) return ctx.notFound("Order not found");
+		if (isLockedForCustomer(order)) return ctx.conflict(ORDER_LOCKED);
 		strapi.log.info("app:v:order-controller: - Removing product from cart", { totalBefore: order.total });
 
 		const updatedCart = [...(order.cart || [])];
@@ -179,14 +210,20 @@ export default factories.createCoreController("api::order.order", ({ strapi }) =
 			updatedCart[existingIndex].count -= count;
 		}
 
+		// A changed cart needs a new checkout: the PayPal order created before can no longer be captured.
 		const orderUnsafe = await strapi.service("api::order.order").update(order.id, {
-			data: { cart: updatedCart },
+			data: { cart: updatedCart, paypalOrderId: null },
 			...orderDefaultParams
 		});
 		strapi.log.info("app:v:order-controller: ✔ Removing product from cart", { totalAfter: order.total });
 		return await sanitize.contentAPI.output(orderUnsafe, strapi.getModel("api::order.order"));
 	},
 
+	/**
+	 * Creates the PayPal order for the order and stores its id on the order: the capture accepts this PayPal order and no other.
+	 * Answers PayPal's id and links, which the shop's PayPal button opens. An order PayPal cannot take, such as one without a usable
+	 * delivery address, is answered 400 with the reason, a cart with a deleted product 409, and a PayPal or network error 502.
+	 */
 	checkout: async (ctx) => {
 		const { uuid } = await sanitize.contentAPI.query(ctx.params, strapi.getModel("api::order.order"));
 		const { returnUrl } = await sanitize.contentAPI.query(ctx.query, strapi.getModel("api::order.order"));
@@ -195,49 +232,68 @@ export default factories.createCoreController("api::order.order", ({ strapi }) =
 			...orderDefaultParams
 		});
 		if (!order) return ctx.notFound("Order not found");
+		if (isLockedForCustomer(order)) return ctx.conflict(ORDER_LOCKED);
 
-		return await paypalApi.createSessionOrThrow(returnUrl as string, order);
+		const missing = missingCheckoutFields(order);
+		if (missing.length > 0) return ctx.badRequest(CHECKOUT_NOT_READY, { missing });
+
+		let session: { id: string; links: unknown };
+		try {
+			session = await paypalApi.createSessionOrThrow(returnUrl as string, order);
+		} catch (error) {
+			const failure = checkoutFailure(error);
+			const fields = { order: order.id, error: describeError(error) };
+			switch (failure.status) {
+				case 400:
+					strapi.log.warn("app:w:order-controller: The order cannot be checked out as it is", fields);
+					return ctx.badRequest(failure.message, { reason: failure.reason });
+				case 409:
+					strapi.log.warn("app:w:order-controller: A product in the cart is no longer available", fields);
+					return ctx.conflict(failure.message);
+				default:
+					strapi.log.error("app:e:order-controller: Could not create the PayPal order", fields);
+					return ctx.badGateway(failure.message);
+			}
+		}
+
+		await strapi.db.query("api::order.order").update({ where: { id: order.id }, data: { paypalOrderId: session.id } });
+		return { id: session.id, links: session.links };
 	},
 
+	/** Captures the PayPal order the checkout stored and marks the order paid, see src/checkout/capture-payment.ts. */
 	capturePayment: async (ctx) => {
 		const { uuid, paypalOrderId } = await sanitize.contentAPI.query(ctx.params, strapi.getModel("api::order.order"));
-		strapi.log.info(`app:i:order-controller: Capturing payment for order ${uuid} with PayPal order ${paypalOrderId}`);
 
-		const order = await strapi.db.query("api::order.order").findOne({
-			where: { uuid },
-			...orderDefaultParams
-		});
-		if (!order) return ctx.notFound("Order not found");
-
-		if (order.paymentAuthorised) {
-			strapi.log.info(`app:i:order-controller: Payment already authorised for order ${uuid}`);
-			return { success: true, alreadyCaptured: true };
-		}
-
-		try {
-			// Capture the payment via PayPal server SDK
-			const captureResult = await paypalApi.checkPaymentStatus({ orderID: paypalOrderId as string });
-
-			if (captureResult.status === "COMPLETED") {
-				// Update order with payment info
-				const updatedOrder = await strapi.entityService.update("api::order.order", order.id, {
-					data: {
-						paymentAuthorised: true,
-						paymentStatus: "authorised",
-						paypalOrderId: paypalOrderId as string
+		const result = await capturePayment(
+			{
+				findOrder: (orderUuid) => strapi.db.query("api::order.order").findOne({ where: { uuid: orderUuid } }),
+				getPayPalOrder: (id) => paypalApi.getOrder(id),
+				capturePayPalOrder: (id, requestId) => paypalApi.captureOrder(id, requestId),
+				// The where clause makes the write conditional: a cart or address change clears paypalOrderId, so an order changed
+				// during the capture is not found, and stays unpaid. Strapi's update answers null then and runs no afterUpdate.
+				updateOrder: (id, storedPayPalOrderId, data) =>
+					strapi.db.query("api::order.order").update({ where: { id, paypalOrderId: storedPayPalOrderId }, data, ...orderDefaultParams }),
+				log: captureLog
 			},
-					...orderDefaultParams
-				});
-
-				strapi.log.info(`app:i:order-controller: Payment captured successfully for order ${uuid}`);
-				return await sanitize.contentAPI.output(updatedOrder, strapi.getModel("api::order.order"));
-			} else {
-				strapi.log.error(`app:e:order-controller: Payment capture failed for order ${uuid}`, { captureResult });
-				return ctx.badRequest("Payment capture failed", { status: captureResult.status });
+			{
+				uuid: typeof uuid === "string" ? uuid : "",
+				paypalOrderId: typeof paypalOrderId === "string" ? paypalOrderId : "",
+				now: new Date()
 			}
-		} catch (error) {
-			strapi.log.error(`app:e:order-controller: Error capturing payment for order ${uuid}`, { error });
-			return ctx.internalServerError("Payment capture failed");
+		);
+
+		switch (result.status) {
+			case 200:
+				if (result.alreadyCaptured === true) return { success: true, alreadyCaptured: true };
+				return await sanitize.contentAPI.output(result.order, strapi.getModel("api::order.order"));
+			case 404:
+				return ctx.notFound(result.message);
+			case 409:
+				return ctx.conflict(result.message);
+			case 502:
+				return ctx.badGateway(result.message);
+			default:
+				return ctx.internalServerError(result.message);
 		}
 	},
 
@@ -245,6 +301,7 @@ export default factories.createCoreController("api::order.order", ({ strapi }) =
 		const { uuid } = await sanitize.contentAPI.query(ctx.params, strapi.getModel("api::order.order"));
 		strapi.log.info(`app:i:order-controller: Started invoice generation`);
 		const orderUnsafe = (await strapi.service("api::order.order").findOneByUuid(uuid)) as Order;
+		if (!orderUnsafe) return ctx.notFound("Order not found");
 
 		if (!orderUnsafe.paymentAuthorised) {
 			return ctx.locked("Payment not authorised, cannot generate invoice");
@@ -263,6 +320,7 @@ export default factories.createCoreController("api::order.order", ({ strapi }) =
 		const { uuid } = await sanitize.contentAPI.query(ctx.params, strapi.getModel("api::order.order"));
 		strapi.log.info(`app:i:order-controller: Started delivery note generation`);
 		const orderUnsafe = (await strapi.service("api::order.order").findOneByUuid(uuid)) as Order;
+		if (!orderUnsafe) return ctx.notFound("Order not found");
 
 		if (!orderUnsafe.paymentAuthorised) {
 			return ctx.locked("Payment not authorised, cannot generate delivery note");
@@ -300,7 +358,7 @@ export default factories.createCoreController("api::order.order", ({ strapi }) =
 		try {
 			return await paypalApi.handleWebhook(ctx.request.body);
 		} catch (error) {
-			strapi.log.error(`paypal-api: ${JSON.stringify({ error })}`);
+			strapi.log.error("app:e:order-controller: Handling the PayPal webhook failed", { error: describeError(error) });
 			return ctx.internalServerError();
 		}
 	}

src/api/order/services/order.ts

@@ -1,7 +1,7 @@
 import path from "path";
 import fs from "fs";
 import { factories } from "@strapi/strapi";
-import { sanitize } from "@strapi/utils";
+import { errors, sanitize } from "@strapi/utils";
 import { ID } from "@strapi/database/dist/types";
 import { vatDecimal, vatIncludedDecimal, baseUrl, adminEmail, shopName, shopContactName, shopAddress, shopPhone, shopEmail, shopLogoUrl, shopSecondaryLogoUrl } from "../../../../config/constants";
 import { calculateTotalProductPrice, productDefaultParams } from "../../product/services/product";
@@ -32,6 +32,7 @@ export default factories.createCoreService("api::order.order", ({ strapi }) => (
 			where: { uuid },
 			...orderDefaultParams
 		});
+		if (!orderUnsafe) return null;
 		orderUnsafe.cart = orderUnsafe?.cart.map((item: CartProduct) => ({
 			...item,
 			product: {
@@ -80,6 +81,7 @@ export default factories.createCoreService("api::order.order", ({ strapi }) => (
 	sendInvoice: async (uuid: string, blob?: any) => {
 		strapi.log.info(`app:i:order-service: - Sending invoice for order ${uuid}`);
 		const oderUnsafe = (await strapi.service("api::order.order").findOneByUuid(uuid)) as Partial<Order>;
+		if (!oderUnsafe) throw new errors.NotFoundError("Order not found");
 
 		const shopContext = { shopName, shopContactName, shopAddress, shopPhone, shopEmail, shopLogoUrl, shopSecondaryLogoUrl };
 		try {
@@ -119,6 +121,7 @@ export default factories.createCoreService("api::order.order", ({ strapi }) => (
 	sendDeliveryNote: async (uuid: string, blob?: ArrayBuffer) => {
 		strapi.log.info(`app:i:order-service: - Sending delivery note for order ${uuid}`);
 		const oderUnsafe = (await strapi.service("api::order.order").findOneByUuid(uuid)) as Partial<Order>;
+		if (!oderUnsafe) throw new errors.NotFoundError("Order not found");
 		const shopContext = { shopName, shopContactName, shopAddress, shopPhone, shopEmail, shopLogoUrl, shopSecondaryLogoUrl };
 		try {
 			const emailConfig: MessageBody = {

src/checkout/capture-payment.ts

@@ -0,0 +1,155 @@
+import { verifyApprovedOrder, verifyCompletedCapture } from "./paypal-verify";
+import type { VerifiableOrder } from "./paypal-verify";
+import { describeError } from "../logging/error";
+
+// POST /orders/:uuid/capture/:paypalOrderId, which the shop calls once the buyer approved the payment in PayPal's window
+// (libreshop/shop pages/checkout/3.vue, onApprove). The PayPal order id comes from the browser, so it must be the one the checkout
+// stored on the order before PayPal is asked anything, and PayPal's answers are checked against the order before it is marked paid.
+// The order controller passes Strapi and PayPalApi as the dependencies; the tests pass fakes.
+
+/** The fields of the order the capture reads. */
+export type CapturableOrder = VerifiableOrder & {
+	id: number | string;
+	paymentAuthorised?: boolean | null;
+	paypalOrderId?: string | null;
+};
+
+/** What a verified capture writes to the order. */
+export type CapturedPayment = {
+	paymentAuthorised: true;
+	paymentStatus: "captured";
+	paypalCaptureId: string;
+	paymentCapturedAt: string;
+};
+
+export type CaptureLog = Record<"info" | "warn" | "error", (message: string, fields: Record<string, unknown>) => void>;
+
+export type CapturePaymentDeps<O extends CapturableOrder, R> = {
+	/** The order with this uuid, or null. */
+	findOrder: (uuid: string) => Promise<O | null>;
+	/** PayPal's order as parsed JSON: GET /v2/checkout/orders/:id. */
+	getPayPalOrder: (paypalOrderId: string) => Promise<unknown>;
+	/** Captures the PayPal order and returns PayPal's order as parsed JSON: POST /v2/checkout/orders/:id/capture. */
+	capturePayPalOrder: (paypalOrderId: string, requestId: string) => Promise<unknown>;
+	/** Writes data to the order only while the order still carries this PayPal order id: the updated order, or null if it does not. */
+	updateOrder: (id: O["id"], paypalOrderId: string, data: CapturedPayment) => Promise<R | null>;
+	log: CaptureLog;
+};
+
+export type CapturePaymentResult<R> =
+	| { status: 200; alreadyCaptured: false; order: R }
+	| { status: 200; alreadyCaptured: true }
+	| { status: 404 | 409 | 500 | 502; message: string };
+
+export const NOT_FOUND = "Order not found";
+export const ALREADY_PAID = "Order is already paid";
+export const NOT_THIS_ORDER = "Payment does not belong to this order";
+export const NOT_MATCHING = "Payment does not match this order";
+export const PAYPAL_FAILED = "PayPal could not capture the payment";
+export const NOT_CONFIRMED = "Payment could not be confirmed";
+export const NOT_RECORDED = "Payment could not be recorded";
+export const ORDER_CHANGED = "Order changed during the payment";
+
+/**
+ * The PayPal-Request-Id of the capture. PayPal answers a repeated id with the first capture's response instead of capturing again,
+ * so a capture that is retried, or sent twice, takes the money once.
+ */
+export const captureRequestId = (uuid: string, paypalOrderId: string): string => `capture-${uuid}-${paypalOrderId}`;
+
+/**
+ * Captures the PayPal order the checkout created for the order and marks the order paid, in this order:
+ * 1. a missing order is answered 404;
+ * 2. a paid order is answered alreadyCaptured if the PayPal order is the one it was paid with, else 409, without a write;
+ * 3. a PayPal order the checkout did not store on the order is answered 409, without asking PayPal;
+ * 4. a PayPal order that is not APPROVED for this order's uuid, total and currency is answered 409, without a capture;
+ * 5. the capture must be COMPLETED for the order total in EUR, else the order stays unpaid and 502 is answered;
+ * 6. the payment is written only while the order still carries this PayPal order id, so a cart or address changed during the
+ *    capture is not marked paid.
+ * PayPal and network errors are answered 502 and logged with name, message and status code only.
+ */
+export const capturePayment = async <O extends CapturableOrder, R>(
+	deps: CapturePaymentDeps<O, R>,
+	{ uuid, paypalOrderId, now }: { uuid: string; paypalOrderId: string; now: Date }
+): Promise<CapturePaymentResult<R>> => {
+	const { log } = deps;
+
+	// An empty uuid finds no order. Strapi would drop an undefined condition and find any order.
+	const order = typeof uuid === "string" && uuid !== "" ? await deps.findOrder(uuid) : null;
+	if (!order) return { status: 404, message: NOT_FOUND };
+
+	const isStoredPayPalOrder = typeof order.paypalOrderId === "string" && order.paypalOrderId !== "" && order.paypalOrderId === paypalOrderId;
+
+	if (order.paymentAuthorised) {
+		if (isStoredPayPalOrder) return { status: 200, alreadyCaptured: true };
+		log.warn("Rejected a capture for a paid order with another PayPal order", { order: order.id });
+		return { status: 409, message: ALREADY_PAID };
+	}
+	if (!isStoredPayPalOrder) {
+		log.warn("Rejected a capture with a PayPal order the checkout did not create for the order", {
+			order: order.id,
+			hasPayPalOrder: typeof order.paypalOrderId === "string" && order.paypalOrderId !== ""
+		});
+		return { status: 409, message: NOT_THIS_ORDER };
+	}
+
+	let paypalOrder: unknown;
+	try {
+		paypalOrder = await deps.getPayPalOrder(paypalOrderId);
+	} catch (error) {
+		log.error("Could not get the PayPal order", { order: order.id, error: describeError(error) });
+		return { status: 502, message: PAYPAL_FAILED };
+	}
+
+	const approved = verifyApprovedOrder(order, paypalOrder);
+	if (approved.ok === false) {
+		log.warn("Rejected a capture: the PayPal order does not match the order", { order: order.id, reason: approved.reason });
+		return { status: 409, message: NOT_MATCHING };
+	}
+
+	let captured: unknown;
+	try {
+		captured = await deps.capturePayPalOrder(paypalOrderId, captureRequestId(order.uuid, paypalOrderId));
+	} catch (error) {
+		log.error("PayPal did not capture the payment", { order: order.id, error: describeError(error) });
+		return { status: 502, message: PAYPAL_FAILED };
+	}
+
+	const capture = verifyCompletedCapture(order, captured);
+	if (capture.ok === false) {
+		// PayPal answered the capture, so it may have taken the money: the PayPal order needs a manual check, and a refund if it was paid.
+		log.error("The PayPal capture does not match the order, which stays unpaid: check the PayPal order for a refund", {
+			order: order.id,
+			reason: capture.reason
+		});
+		return { status: 502, message: NOT_CONFIRMED };
+	}
+
+	const data: CapturedPayment = {
+		paymentAuthorised: true,
+		paymentStatus: "captured",
+		paypalCaptureId: capture.captureId,
+		paymentCapturedAt: now.toISOString()
+	};
+
+	let updated: R | null;
+	try {
+		updated = await deps.updateOrder(order.id, paypalOrderId, data);
+	} catch (error) {
+		log.error("PayPal captured the payment, but the order could not be marked paid: check the order", {
+			order: order.id,
+			capture: capture.captureId,
+			error: describeError(error)
+		});
+		return { status: 500, message: NOT_RECORDED };
+	}
+	if (updated === null || updated === undefined) {
+		log.error("PayPal captured the payment, but the order changed during the capture and stays unpaid: check the order for a refund", {
+			order: order.id,
+			capture: capture.captureId
+		});
+		return { status: 409, message: ORDER_CHANGED };
+	}
+
+	log.info("Captured the payment", { order: order.id, capture: capture.captureId });
+	return { status: 200, alreadyCaptured: false, order: updated };
+};

src/checkout/customer-update.ts

@@ -0,0 +1,146 @@
+// What a customer may write to an order: the fields of the shop's checkout steps, and nothing else.
+// The shop forwards the browser's body unchanged (libreshop/shop server/api/orders/[uuid].put.ts), so the body is untrusted.
+// Step 1 (pages/checkout/1.vue) sends { data: { email, acceptedTermsAndConditionsAt } }, step 2 (pages/checkout/2.vue) sends
+// { data: { invoiceAddress, deliveryAddress, invoiceAddressStructured, deliveryAddressStructured, delivery } }.
+// Payment state, totals, numbers, documents, the cart and the customer are written by the server alone. A body that sends any
+// of them is rejected as a whole instead of stripped, so a client that relies on such a write fails visibly.
+
+/** The attributes of the address.structured-address component (src/components/address/structured-address.json). */
+const STRUCTURED_ADDRESS_FIELDS = ["givenName", "familyName", "streetAddress", "postalCode", "addressLevel2", "country"] as const;
+
+export type CustomerStructuredAddress = Partial<Record<(typeof STRUCTURED_ADDRESS_FIELDS)[number], string | null>>;
+
+/** The order fields a customer may set, each optional. */
+export type CustomerUpdate = {
+	email?: string;
+	acceptedTermsAndConditionsAt?: string;
+	invoiceAddress?: string;
+	deliveryAddress?: string;
+	invoiceAddressStructured?: CustomerStructuredAddress;
+	deliveryAddressStructured?: CustomerStructuredAddress;
+	delivery?: number;
+};
+
+/**
+ * errors: one message per rejected field, which names the field and never repeats its value.
+ * fields: the names of the rejected fields alone, for the log.
+ */
+export type CustomerUpdateResult = { ok: true; data: CustomerUpdate } | { ok: false; errors: string[]; fields: string[] };
+
+// The longest address an SMTP path of 256 octets, angle brackets included, can carry (RFC 5321).
+const MAX_EMAIL_LENGTH = 254;
+const MAX_ADDRESS_LENGTH = 500;
+const MAX_ADDRESS_COMPONENT_LENGTH = 200;
+// Strapi's ids are Postgres integer columns: a larger number makes the query fail instead of finding nothing.
+const MAX_ID = 2147483647;
+// Rejected keys are chosen by the client and end up in the response and the log, so a long one is cut.
+const MAX_KEY_LENGTH = 64;
+
+const isObject = (value: unknown): value is Record<string, unknown> => typeof value === "object" && value !== null && !Array.isArray(value);
+
+const keyName = (key: string): string => (key.length > MAX_KEY_LENGTH ? `${key.slice(0, MAX_KEY_LENGTH)}…` : key);
+
+const isStructuredAddressField = (key: string): key is (typeof STRUCTURED_ADDRESS_FIELDS)[number] =>
+	(STRUCTURED_ADDRESS_FIELDS as readonly string[]).includes(key);
+
+// An "@" with something on both sides, and no whitespace or control character: the invoice is mailed to this address.
+const isEmail = (email: string): boolean => {
+	const at = email.lastIndexOf("@");
+	return email.length <= MAX_EMAIL_LENGTH && at > 0 && at < email.length - 1 && !/[\s\u0000-\u001f\u007f]/.test(email);
+};
+
+const isText = (value: unknown, maxLength: number): value is string => typeof value === "string" && value.length <= maxLength;
+
+// The shop's form sends every component as a string (pages/checkout/2.vue, mapToStructuredAddress), but it fills the form from
+// the stored address, whose unset components Strapi returns as null. Every component of the address is optional.
+const isAddressComponent = (value: unknown): value is string | null => value === null || isText(value, MAX_ADDRESS_COMPONENT_LENGTH);
+
+/**
+ * Checks the body of PUT /orders/:uuid/cart. Returns the fields to write, or why the body is rejected.
+ * `now` is the server's time, recorded as the time the customer accepted the terms.
+ */
+export const parseCustomerUpdate = (body: unknown, now: Date): CustomerUpdateResult => {
+	const rejected: { field: string; reason: string }[] = [];
+	const reject = (field: string, reason: string) => {
+		rejected.push({ field, reason });
+	};
+	const data: CustomerUpdate = {};
+
+	const parseStructuredAddress = (field: string, value: unknown): CustomerStructuredAddress | undefined => {
+		if (!isObject(value)) {
+			reject(field, "must be an object");
+			return undefined;
+		}
+		const address: CustomerStructuredAddress = {};
+		let valid = true;
+		for (const key of Object.keys(value)) {
+			const component = value[key];
+			if (!isStructuredAddressField(key)) {
+				reject(`${field}.${keyName(key)}`, "not a structured address field");
+				valid = false;
+			} else if (isAddressComponent(component)) {
+				address[key] = component;
+			} else {
+				reject(`${field}.${key}`, `must be a string of at most ${MAX_ADDRESS_COMPONENT_LENGTH} characters, or null`);
+				valid = false;
+			}
+		}
+		return valid ? address : undefined;
+	};
+
+	if (!isObject(body)) {
+		reject("body", "must be an object of the form { data: { … } }");
+	} else {
+		for (const key of Object.keys(body)) {
+			if (key !== "data") reject(keyName(key), "not accepted, the fields belong in data");
+		}
+
+		const fields = body.data;
+		if (fields === undefined) {
+			reject("data", "missing");
+		} else if (!isObject(fields)) {
+			reject("data", "must be an object");
+		} else {
+			for (const key of Object.keys(fields)) {
+				const value = fields[key];
+				switch (key) {
+					case "email": {
+						const email = typeof value === "string" ? value.trim() : "";
+						if (isEmail(email)) data.email = email;
+						else reject("data.email", `must be an email address of at most ${MAX_EMAIL_LENGTH} characters`);
+						break;
+					}
+					case "acceptedTermsAndConditionsAt":
+						// The invoice is dated by this time: it is the Ausstellungsdatum in the invoice PDF (the order service's
+						// defaultPdfBody) and in the invoice email (src/templates/emailTemplates.ts). The client's clock and value
+						// are ignored, so that no client can backdate or postdate an invoice.
+						if (value) data.acceptedTermsAndConditionsAt = now.toISOString();
+						else reject("data.acceptedTermsAndConditionsAt", "must be sent only to accept the terms, as true or a timestamp");
+						break;
+					case "invoiceAddress":
+					case "deliveryAddress":
+						if (isText(value, MAX_ADDRESS_LENGTH)) data[key] = value;
+						else reject(`data.${key}`, `must be a string of at most ${MAX_ADDRESS_LENGTH} characters`);
+						break;
+					case "invoiceAddressStructured":
+					case "deliveryAddressStructured": {
+						const address = parseStructuredAddress(`data.${key}`, value);
+						if (address) data[key] = address;
+						break;
+					}
+					case "delivery":
+						if (typeof value === "number" && Number.isInteger(value) && value > 0 && value <= MAX_ID) data.delivery = value;
+						else reject("data.delivery", "must be the id of a delivery method, a positive integer");
+						break;
+					default:
+						reject(`data.${keyName(key)}`, "not a field the customer may set");
+				}
+			}
+		}
+	}
+
+	if (rejected.length > 0) {
+		return { ok: false, errors: rejected.map(({ field, reason }) => `${field}: ${reason}`), fields: rejected.map(({ field }) => field) };
+	}
+	return { ok: true, data };
+};

src/checkout/order-state.ts

@@ -0,0 +1,27 @@
+/** The fields of an order that decide whether the customer may still change it. */
+export type OrderLockState = {
+	paymentAuthorised?: boolean | null;
+};
+
+/**
+ * Once its payment is authorised, the order is what the customer paid for and what the invoice is generated from,
+ * so the customer can no longer change its contact details, addresses, delivery method or cart.
+ */
+export const isLockedForCustomer = (order: OrderLockState): boolean => Boolean(order.paymentAuthorised);
+
+/** The fields of an order a checkout needs: the contact and address steps of the shop's checkout, and a delivery method. */
+export type CheckoutFields = {
+	email?: string | null;
+	invoiceAddress?: string | null;
+	/** The populated delivery method, or null. */
+	delivery?: unknown;
+};
+
+/** The names of the fields the order still lacks for a checkout, in this order: email, invoiceAddress, delivery. [] if none. */
+export const missingCheckoutFields = (order: CheckoutFields): string[] => {
+	const missing: string[] = [];
+	if (typeof order.email !== "string" || order.email.trim() === "") missing.push("email");
+	if (typeof order.invoiceAddress !== "string" || order.invoiceAddress.trim() === "") missing.push("invoiceAddress");
+	if (order.delivery === null || order.delivery === undefined) missing.push("delivery");
+	return missing;
+};

src/checkout/paypal-client.ts

@@ -0,0 +1,96 @@
+import type { Configuration, Environment } from "@paypal/paypal-server-sdk";
+
+// The PayPal SDK client behind PayPalApi, created through a factory so that it can be replaced: PayPalApi passes one that creates
+// the SDK's Client and OrdersController, the tests a fake.
+//
+// The SDK keeps the promise of its OAuth token for the lifetime of a Client, also when the token request failed: every later call
+// awaits the same rejected promise and fails with the same error without a request, until the process restarts. One failed token
+// request, during a DNS outage for example, stopped every checkout until a restart.
+
+/** The SDK's default timeout is 0, which means none: a call to PayPal that hangs would hang the checkout with it. */
+export const PAYPAL_TIMEOUT_MS = 15000;
+
+/**
+ * The configuration of the SDK's Client. The SDK logs method, URL and status of each request to the console, but no bodies, since
+ * a request body holds the buyer's name and address, and no headers, since they hold the token.
+ */
+export const paypalClientConfiguration = ({
+	clientId,
+	clientSecret,
+	environment
+}: {
+	clientId: string;
+	clientSecret: string;
+	environment: Environment;
+}): Partial<Configuration> => ({
+	clientCredentialsAuthCredentials: {
+		oAuthClientId: clientId,
+		oAuthClientSecret: clientSecret
+	},
+	timeout: PAYPAL_TIMEOUT_MS,
+	environment,
+	logging: {
+		logRequest: { logBody: false, logHeaders: false },
+		logResponse: { logBody: false, logHeaders: false }
+	}
+});
+
+const TOKEN_PATH = "/v1/oauth2/token";
+
+/** The URL of the request the error belongs to: an error of the SDK carries the request, an axios error its config. */
+const requestUrl = (error: object): string => {
+	const { request, config } = error as { request?: { url?: unknown }; config?: { url?: unknown } };
+	const url = request?.url ?? config?.url;
+	return typeof url === "string" ? url : "";
+};
+
+/**
+ * Whether the error may leave the client unusable, so that the next call needs a new one: any error of the token request, which
+ * the SDK keeps; an error without an answer from PayPal (network, DNS, timeout); 401, a token PayPal no longer accepts; and 5xx.
+ * PayPal's other answers, such as 422 for an order it rejects, leave the client as it is.
+ */
+export const breaksClient = (error: unknown): boolean => {
+	if (typeof error !== "object" || error === null) return true;
+	const { statusCode } = error as { statusCode?: unknown };
+	if (typeof statusCode !== "number") return true;
+	if (statusCode === 401 || statusCode >= 500) return true;
+	return requestUrl(error).includes(TOKEN_PATH);
+};
+
+export type PayPalClient<C> = {
+	/** Runs the request on the current controller. An error that breaksClient replaces the controller for the calls after it. */
+	call<T>(request: (controller: C) => Promise<T>): Promise<T>;
+};
+
+/**
+ * Creates the controller on the first call, and a new one, with a new client and token, on the first call after an error that
+ * breaksClient. onReplace is called with that error.
+ */
+export const createPayPalClient = <C>({
+	configuration,
+	createController,
+	onReplace
+}: {
+	configuration: Partial<Configuration>;
+	createController: (configuration: Partial<Configuration>) => C;
+	onReplace?: (error: unknown) => void;
+}): PayPalClient<C> => {
+	let current: C | undefined;
+
+	return {
+		async call<T>(request: (controller: C) => Promise<T>): Promise<T> {
+			current ??= createController(configuration);
+			const controller = current;
+			try {
+				return await request(controller);
+			} catch (error) {
+				// A call that failed on a controller which was replaced meanwhile leaves its successor alone.
+				if (breaksClient(error) && current === controller) {
+					current = undefined;
+					onReplace?.(error);
+				}
+				throw error;
+			}
+		}
+	};
+};

src/checkout/paypal-order.ts

@@ -1,20 +1,30 @@
-import type { Order } from "../../types";
-import { calculateTotalProductPrice } from "./pricing";
+import type { CustomerStructuredAddress } from "./customer-update";
 import { vatIncludedDecimal } from "./vat";
 
 // The PayPal order that PayPalApi.createSessionOrThrow creates, built without the PayPal SDK so it can be unit tested.
 // String literals stand in for the SDK enums, with the values of @paypal/paypal-server-sdk 0.6.1.
+//
+// The request sends no items. With items, PayPal requires item_total to be the sum of unit_amount × quantity and tax_total the
+// sum of tax × quantity, and amounts rounded per unit miss the net and the VAT of the subtotal, which the invoice states:
+// 3 × 12.50 gives 3 × 10.50 = 31.50 net and 3 × 2.00 = 6.00 tax, the subtotal of 37.50 gives 31.51 net and 5.99 VAT.
 
 export type PayPalMoney = {
 	currencyCode: string;
 	value: string;
 };
 
-export type PayPalOrderItem = {
-	name: string;
-	unitAmount: PayPalMoney;
-	tax: PayPalMoney;
-	quantity: string;
+export type PayPalShipping = {
+	name: { fullName: string };
+	address: { addressLine1: string; addressLine2?: string; postalCode: string; adminArea2: string; countryCode: string };
+};
+
+export type PayPalBreakdown = {
+	itemTotal: PayPalMoney;
+	taxTotal: PayPalMoney;
+	/** Undefined for an order without a delivery method. */
+	shipping: PayPalMoney | undefined;
+	/** The surcharge of the payment method, only when it is above 0. */
+	handling?: PayPalMoney;
 };
 
 export type PayPalOrderRequest = {
@@ -22,17 +32,8 @@ export type PayPalOrderRequest = {
 	intent: "CAPTURE";
 	purchaseUnits: {
 		referenceId: string;
-		amount: PayPalMoney & {
-			breakdown: {
-				itemTotal: PayPalMoney;
-				taxTotal: PayPalMoney;
-				shipping: PayPalMoney | undefined;
-			};
-		};
-		shipping: {
-			name: { fullName: string };
-			address: { addressLine1: string; postalCode: string; adminArea2: string; countryCode: string };
-		};
+		amount: PayPalMoney & { breakdown: PayPalBreakdown };
+		shipping: PayPalShipping;
 		customId: string;
 		invoiceId: string;
 	}[];
@@ -45,73 +46,191 @@ export type PayPalOrderRequest = {
 };
 
 /**
- * The part of PayPalApi.createSessionOrThrow that runs before its try block, so nothing thrown here is logged there.
- * Rejects an order without a total, then computes one item per cart line. The items are not sent to PayPal, but computing
- * them throws a TypeError for a cart line without a product.
+ * The fields of the order the request is built from, as the checkout reads the order (strapi.db.query findOne with
+ * orderDefaultParams). Each of them may be null. Prices are decimals, which Strapi returns as numbers.
  */
-export const buildPayPalOrderItems = (order: Order): PayPalOrderItem[] => {
-	if (!order.total) throw new Error("Cart is empty or has no total");
+export type PayPalOrderSource = {
+	uuid: string;
+	invoiceNumber?: string | null;
+	subtotal?: number | string | null;
+	total?: number | string | null;
+	VAT?: number | string | null;
+	delivery?: { price?: number | string | null } | null;
+	payment?: { price?: number | string | null } | null;
+	cart?: ({ product?: unknown } | null)[] | null;
+	deliveryAddress?: string | null;
+	deliveryAddressStructured?: CustomerStructuredAddress | null;
+	invoiceAddressStructured?: CustomerStructuredAddress | null;
+};
 
-	return order.cart.map((item) => {
-		const totalProductPrice = calculateTotalProductPrice(item.product);
-		const amount = totalProductPrice / vatIncludedDecimal;
-		const tax = totalProductPrice - amount;
+/** The order lacks something PayPal needs, or its totals do not add up, so the customer has to complete or change it first. */
+export class CheckoutNotReadyError extends Error {
+	constructor(message: string) {
+		super(message);
+		this.name = "CheckoutNotReadyError";
+	}
+}
+
+/** A cart line whose product was deleted. */
+export class ProductUnavailableError extends Error {
+	constructor(message: string) {
+		super(message);
+		this.name = "ProductUnavailableError";
+	}
+}
+
+export const CHECKOUT_NOT_READY = "Order is not ready for checkout";
+export const PRODUCT_UNAVAILABLE = "A product in the cart is no longer available";
+export const PAYPAL_ORDER_FAILED = "Could not create the PayPal order";
+
+export type CheckoutFailure = { status: 400; message: string; reason: string } | { status: 409 | 502; message: string };
+
+/**
+ * The checkout's answer to an error of PayPalApi.createSessionOrThrow: 400 with the reason for an order that is not ready, 409 for a
+ * product that is no longer available. Any other error is PayPal's or the network's: 502.
+ */
+export const checkoutFailure = (error: unknown): CheckoutFailure => {
+	if (error instanceof CheckoutNotReadyError) return { status: 400, message: CHECKOUT_NOT_READY, reason: error.message };
+	if (error instanceof ProductUnavailableError) return { status: 409, message: PRODUCT_UNAVAILABLE };
+	return { status: 502, message: PAYPAL_ORDER_FAILED };
+};
+
+// Money is computed in whole cents.
+
+/** A decimal amount of euros as whole cents, or null for anything that is not a finite number. */
+const toCents = (amount: unknown): number | null => {
+	const value = typeof amount === "string" && amount.trim() !== "" ? Number(amount) : amount;
+	return typeof value === "number" && Number.isFinite(value) ? Math.round(value * 100) : null;
+};
+
+/** Whole, non-negative cents as PayPal money: 1504 is "15.04". */
+const money = (cents: number): PayPalMoney => ({
+	currencyCode: "EUR",
+	value: `${Math.floor(cents / 100)}.${String(cents % 100).padStart(2, "0")}`
+});
+
+// vatIncludedDecimal as a whole percentage (119), so that the net of the subtotal is a quotient of whole numbers.
+const VAT_INCLUDED_PERCENT = Math.round(vatIncludedDecimal * 100);
+
+/**
+ * The breakdown of the order's total: the net of its subtotal, its VAT, the price of its delivery method, 0 when that price is not
+ * set, and the surcharge of its payment method as handling, which the order service adds to the total. PayPal rejects a breakdown
+ * that does not add up to the amount, which happens when a price changed after the order service computed the totals, so such an
+ * order is rejected here.
+ */
+const breakdownFor = (order: PayPalOrderSource, totalCents: number): PayPalBreakdown => {
+	const subtotalCents = toCents(order.subtotal);
+	const taxCents = toCents(order.VAT);
+	if (subtotalCents === null || taxCents === null) throw new CheckoutNotReadyError("The order has no subtotal or no VAT");
+
+	const itemTotalCents = Math.round((subtotalCents * 100) / VAT_INCLUDED_PERCENT);
+	const shippingCents = order.delivery ? (toCents(order.delivery.price) ?? 0) : undefined;
+	const surchargeCents = toCents(order.payment?.price) ?? 0;
+
+	const parts = [itemTotalCents, taxCents, shippingCents ?? 0, surchargeCents];
+	const sum = parts.reduce((a, b) => a + b, 0);
+	if (parts.some((cents) => cents < 0) || sum !== totalCents) {
+		throw new CheckoutNotReadyError(
+			`The order's totals do not add up: total ${totalCents} cents, items ${itemTotalCents} + VAT ${taxCents} + shipping ${shippingCents ?? 0} + surcharge ${surchargeCents}`
+		);
+	}
 
 	return {
-			name: item.product.name,
-			unitAmount: {
-				currencyCode: "EUR",
-				value: amount.toFixed(2)
-			},
-			tax: {
-				currencyCode: "EUR",
-				value: tax.toFixed(2)
-			},
-			quantity: item.count.toString()
+		itemTotal: money(itemTotalCents),
+		taxTotal: money(taxCents),
+		shipping: shippingCents === undefined ? undefined : money(shippingCents),
+		...(surchargeCents > 0 ? { handling: money(surchargeCents) } : {})
 	};
-	});
+};
+
+const text = (value: unknown): string => (typeof value === "string" ? value.trim() : "");
+
+const STRUCTURED_COMPONENTS = ["givenName", "familyName", "streetAddress", "postalCode", "addressLevel2"] as const;
+
+/** Whether any component besides the country is set: Strapi stores the country with the default DE. */
+const isEntered = (address: CustomerStructuredAddress | null | undefined): boolean =>
+	typeof address === "object" && address !== null && STRUCTURED_COMPONENTS.some((key) => text(address[key]) !== "");
+
+/** The shipping address from a structured address, which needs a name, a street, a postal code and a city. */
+const fromStructured = (field: string, address: CustomerStructuredAddress): PayPalShipping => {
+	const fullName = [text(address.givenName), text(address.familyName)].filter((part) => part !== "").join(" ");
+	const addressLine1 = text(address.streetAddress);
+	const postalCode = text(address.postalCode);
+	const adminArea2 = text(address.addressLevel2);
+	const countryCode = (text(address.country) || "DE").toUpperCase();
+
+	const lacking = [
+		[fullName, "givenName and familyName"],
+		[addressLine1, "streetAddress"],
+		[postalCode, "postalCode"],
+		[adminArea2, "addressLevel2"]
+	]
+		.filter(([value]) => value === "")
+		.map(([, component]) => component);
+	if (lacking.length > 0) throw new CheckoutNotReadyError(`${field} lacks ${lacking.join(", ")}`);
+	if (!/^[A-Z]{2}$/.test(countryCode)) throw new CheckoutNotReadyError(`${field} has no two-letter country code`);
+
+	return { name: { fullName }, address: { addressLine1, postalCode, adminArea2, countryCode } };
 };
 
 /**
- * The order request body PayPalApi.createSessionOrThrow sends. It is built inside that try block, so whatever throws here is logged there.
+ * The shipping address from a text address as the shop writes it (libreshop/shop pages/checkout/2.vue, addressToString): the name,
+ * the street and "<postal code> <city>" on lines of their own. Lines between the name and the street, such as c/o, become
+ * addressLine2. Blank lines are skipped. The country is DE.
  */
-export const buildPayPalOrderRequest = (returnUrl: string, order: Order): PayPalOrderRequest => ({
+const fromText = (field: string, address: string): PayPalShipping => {
+	const lines = address
+		.split(/\r\n|\r|\n/)
+		.map((line) => line.trim())
+		.filter((line) => line !== "");
+	if (lines.length < 3) throw new CheckoutNotReadyError(`${field} needs the name, the street, and the postal code and city on lines of their own`);
+
+	const city = /^(\S+)\s+(\S.*)$/.exec(lines[lines.length - 1]);
+	if (city === null) throw new CheckoutNotReadyError(`The last line of ${field} is not the postal code and the city`);
+
+	const addressLine2 = lines.slice(1, -2).join(", ");
+	return {
+		name: { fullName: lines[0] },
+		address: {
+			addressLine1: lines[lines.length - 2],
+			...(addressLine2 !== "" ? { addressLine2 } : {}),
+			postalCode: city[1],
+			adminArea2: city[2],
+			countryCode: "DE"
+		}
+	};
+};
+
+/**
+ * The address PayPal shows the buyer as the shipping address: the structured delivery address, else the structured invoice address,
+ * else the text delivery address. The shop sends the invoice address as the delivery address when the buyer gives no other. An
+ * address that is entered but incomplete is rejected rather than replaced by the next one.
+ */
+const shippingFor = (order: PayPalOrderSource): PayPalShipping => {
+	if (isEntered(order.deliveryAddressStructured)) return fromStructured("deliveryAddressStructured", order.deliveryAddressStructured);
+	if (isEntered(order.invoiceAddressStructured)) return fromStructured("invoiceAddressStructured", order.invoiceAddressStructured);
+	if (text(order.deliveryAddress) !== "") return fromText("deliveryAddress", order.deliveryAddress);
+	throw new CheckoutNotReadyError("The order has no delivery address");
+};
+
+/**
+ * The order request body PayPalApi.createSessionOrThrow sends. Throws ProductUnavailableError for a cart line whose product was
+ * deleted, and CheckoutNotReadyError for an empty cart, a missing total, totals that do not add up or a missing or unusable
+ * delivery address. The messages name fields and amounts, never an address.
+ */
+export const buildPayPalOrderRequest = (returnUrl: string, order: PayPalOrderSource): PayPalOrderRequest => {
+	const cart = Array.isArray(order.cart) ? order.cart : [];
+	const totalCents = toCents(order.total);
+	if (cart.length === 0 || totalCents === null || totalCents <= 0) throw new CheckoutNotReadyError("Cart is empty or has no total");
+	if (cart.some((line) => !line?.product)) throw new ProductUnavailableError(PRODUCT_UNAVAILABLE);
+
+	return {
 		intent: "CAPTURE",
 		purchaseUnits: [
 			{
-			// items: computed by buildPayPalOrderItems, but not sent
 				referenceId: order.uuid,
-			amount: {
-				currencyCode: "EUR",
-				value: order.total.toFixed(2),
-				breakdown: {
-					itemTotal: {
-						currencyCode: "EUR",
-						value: (Math.round((order.subtotal / vatIncludedDecimal) * 100) / 100).toFixed(2)
-					},
-					taxTotal: {
-						currencyCode: "EUR",
-						value: order.VAT.toFixed(2)
-					},
-					shipping: order.delivery
-						? {
-								currencyCode: "EUR",
-								value: order.delivery.price.toFixed(2)
-							}
-						: undefined
-				}
-			},
-			shipping: {
-				name: {
-					fullName: order.deliveryAddress.split("\n")[0]
-				},
-				address: {
-					addressLine1: order.deliveryAddress.split("\n")[1],
-					postalCode: order.deliveryAddress.split("\n")[2].slice(0, 5),
-					adminArea2: order.deliveryAddress.split("\n")[2].slice(6),
-					countryCode: "DE"
-				}
-			},
+				amount: { ...money(totalCents), breakdown: breakdownFor(order, totalCents) },
+				shipping: shippingFor(order),
 				customId: order.uuid,
 				invoiceId: order.invoiceNumber
 			}
@@ -121,4 +240,5 @@ export const buildPayPalOrderRequest = (returnUrl: string, order: Order): PayPal
 			cancelUrl: returnUrl,
 			shippingPreference: "SET_PROVIDED_ADDRESS"
 		}
-});
+	};
+};

src/checkout/paypal-verify.ts

@@ -0,0 +1,104 @@
+// Checks PayPal's answers against the shop order before the order is marked paid: the PayPal order the buyer approved
+// (GET /v2/checkout/orders/:id) and the order after its capture (POST /v2/checkout/orders/:id/capture, Prefer: return=representation).
+// The JSON is PayPal's Orders v2 JSON in snake_case, as PayPalApi parses the raw response body. Money is compared in integer cents.
+// A reason says what does not match. It repeats only PayPal's statuses, currency codes and amounts, never a name, an email address
+// or an address from the response, because it is logged.
+
+/** The fields of the shop order the checks compare. */
+export type VerifiableOrder = {
+	uuid: string;
+	total: number | null;
+};
+
+export type ApprovedOrderCheck = { ok: true } | { ok: false; reason: string };
+
+export type CompletedCaptureCheck = { ok: true; captureId: string } | { ok: false; reason: string };
+
+const CURRENCY = "EUR";
+
+type Json = Record<string, unknown>;
+
+const isObject = (value: unknown): value is Json => typeof value === "object" && value !== null && !Array.isArray(value);
+
+/** PayPal's money value as integer cents: "12.34" is 1234. Null for anything but a non-negative amount with at most two decimals. */
+export const parseCents = (value: unknown): number | null => {
+	if (typeof value !== "string") return null;
+	const match = /^(\d{1,10})(?:\.(\d{1,2}))?$/.exec(value);
+	if (match === null) return null;
+	return Number(match[1]) * 100 + Number((match[2] ?? "").padEnd(2, "0"));
+};
+
+/** The order total in integer cents, or null if the order has no positive total. Strapi returns the decimal column as a number. */
+export const orderTotalCents = (order: { total: number | null }): number | null =>
+	typeof order.total === "number" && Number.isFinite(order.total) && order.total > 0 ? Math.round(order.total * 100) : null;
+
+const formatCents = (cents: number): string => `${Math.floor(cents / 100)}.${String(cents % 100).padStart(2, "0")}`;
+
+// The values of OrderStatus and CaptureStatus in @paypal/paypal-server-sdk 0.6.1. A reason repeats these and ISO currency codes,
+// and no other value from the response.
+const ORDER_STATUSES = ["CREATED", "SAVED", "APPROVED", "VOIDED", "COMPLETED", "PAYER_ACTION_REQUIRED"];
+const CAPTURE_STATUSES = ["COMPLETED", "DECLINED", "PARTIALLY_REFUNDED", "PENDING", "REFUNDED", "FAILED"];
+
+const shown = (value: unknown, isKnown: (value: string) => boolean): string =>
+	typeof value === "string" && isKnown(value) ? value : "missing or unexpected";
+const orderStatus = (value: unknown): string => shown(value, (status) => ORDER_STATUSES.includes(status));
+const captureStatus = (value: unknown): string => shown(value, (status) => CAPTURE_STATUSES.includes(status));
+const currency = (value: unknown): string => shown(value, (code) => /^[A-Z]{3}$/.test(code));
+
+const firstPurchaseUnit = (paypalOrder: Json): Json | null => {
+	const units = paypalOrder.purchase_units;
+	return Array.isArray(units) && isObject(units[0]) ? units[0] : null;
+};
+
+/** Why PayPal's money ({ currency_code, value }) is not the order total in EUR, or null if it is. */
+const amountMismatch = (subject: string, money: unknown, order: VerifiableOrder): string | null => {
+	if (!isObject(money)) return `${subject} has no amount`;
+	if (money.currency_code !== CURRENCY) return `${subject} currency is ${currency(money.currency_code)}, not ${CURRENCY}`;
+	const cents = parseCents(money.value);
+	if (cents === null) return `${subject} amount is not a money value`;
+	const total = orderTotalCents(order);
+	if (total === null) return "the order has no total";
+	if (cents !== total) return `${subject} amount ${formatCents(cents)} is not the order total ${formatCents(total)}`;
+	return null;
+};
+
+/**
+ * The PayPal order may be captured for this order: the buyer approved it, it was created for this order (its custom_id is the
+ * order's uuid, see buildPayPalOrderRequest), and its amount is the order total in EUR.
+ */
+export const verifyApprovedOrder = (order: VerifiableOrder, paypalOrder: unknown): ApprovedOrderCheck => {
+	if (!isObject(paypalOrder)) return { ok: false, reason: "the PayPal order is not an object" };
+	if (paypalOrder.status !== "APPROVED") {
+		return { ok: false, reason: `the PayPal order status is ${orderStatus(paypalOrder.status)}, not APPROVED` };
+	}
+
+	const unit = firstPurchaseUnit(paypalOrder);
+	if (unit === null) return { ok: false, reason: "the PayPal order has no purchase unit" };
+	if (typeof order.uuid !== "string" || order.uuid === "" || unit.custom_id !== order.uuid) {
+		return { ok: false, reason: "the custom_id of the PayPal order is not the order's uuid" };
+	}
+
+	const mismatch = amountMismatch("the PayPal order", unit.amount, order);
+	return mismatch === null ? { ok: true } : { ok: false, reason: mismatch };
+};
+
+/**
+ * PayPal captured the order total in EUR: the PayPal order and its first capture are COMPLETED. Returns the capture's id.
+ * A capture PayPal holds for review (PENDING) or declined (DECLINED) is not a payment.
+ */
+export const verifyCompletedCapture = (order: VerifiableOrder, captured: unknown): CompletedCaptureCheck => {
+	if (!isObject(captured)) return { ok: false, reason: "the capture response is not an object" };
+	if (captured.status !== "COMPLETED") return { ok: false, reason: `the PayPal order status is ${orderStatus(captured.status)}, not COMPLETED` };
+
+	const unit = firstPurchaseUnit(captured);
+	const payments = unit !== null && isObject(unit.payments) ? unit.payments : null;
+	const capture = payments !== null && Array.isArray(payments.captures) && isObject(payments.captures[0]) ? payments.captures[0] : null;
+	if (capture === null) return { ok: false, reason: "the capture response has no capture" };
+	if (capture.status !== "COMPLETED") return { ok: false, reason: `the capture status is ${captureStatus(capture.status)}, not COMPLETED` };
+
+	const mismatch = amountMismatch("the capture", capture.amount, order);
+	if (mismatch !== null) return { ok: false, reason: mismatch };
+	if (typeof capture.id !== "string" || !/^[A-Za-z0-9-]{1,64}$/.test(capture.id)) return { ok: false, reason: "the capture has no valid id" };
+
+	return { ok: true, captureId: capture.id };
+};

src/logging/error.ts

@@ -0,0 +1,30 @@
+/** What is logged of an error. */
+export type ErrorSummary = {
+	name: string;
+	message: string;
+	statusCode: number | undefined;
+};
+
+// A message is cut to its first line and to this length: the PayPal SDK's ResponseValidationError quotes the response values it
+// rejected on the lines after its first.
+const MAX_LENGTH = 200;
+
+const cut = (text: string): string => {
+	const line = text.split("\n")[0];
+	return line.length > MAX_LENGTH ? `${line.slice(0, MAX_LENGTH)}…` : line;
+};
+
+/**
+ * The name, the first line of the message and the HTTP status code of an error, and nothing else. An error of the PayPal SDK
+ * (ApiError) or of axios carries its request, whose Authorization header holds the PayPal client credentials or an access token,
+ * so the error object itself is never logged.
+ */
+export const describeError = (error: unknown): ErrorSummary => {
+	if (typeof error !== "object" || error === null) return { name: typeof error, message: "", statusCode: undefined };
+	const { name, message, statusCode } = error as { name?: unknown; message?: unknown; statusCode?: unknown };
+	return {
+		name: typeof name === "string" ? cut(name) : "object",
+		message: typeof message === "string" ? cut(message) : "",
+		statusCode: typeof statusCode === "number" ? statusCode : undefined
+	};
+};

src/logging/format.ts

@@ -1,3 +1,5 @@
+import { describeError } from "./error";
+
 /** What winston hands a printf template (logform's TransformableInfo); Strapi's default format has added `timestamp`. */
 export type LogInfo = {
 	level: string;
@@ -5,10 +7,76 @@ export type LogInfo = {
 	[key: string | symbol]: unknown;
 };
 
-/** One console line: `<timestamp>Z <level>: <message> <all other fields as indented JSON, if any>`. */
-export const formatLogLine = ({ timestamp, level, message, ...rest }: LogInfo): string => {
-	let restString = JSON.stringify(rest, undefined, 2);
+export type LogFormatOptions = {
+	/** Writes the stack of an error value too. config/logger.ts sets it at the debug level, the local one. */
+	stack?: boolean;
+};
+
+// A field whose name matches holds a credential or a session, at any depth: an axios error carries the request headers in
+// config.headers, among them "Authorization: Basic <base64 of the PayPal client id and secret>".
+const SENSITIVE_KEY = /authorization|cookie|password|secret|token|api[-_]?key/i;
+const REDACTED = "[redacted]";
+
+/**
+ * A copy of the value that JSON.stringify writes without throwing and without credentials:
+ * - a field whose name matches SENSITIVE_KEY becomes "[redacted]";
+ * - an Error becomes { name, message } as describeError has them, the first line of the message only, plus the stack if asked;
+ * - an object that contains itself is written once, the reference to it as "[Circular]";
+ * - an instance of a class other than Object and Array is written as its toJSON() if it has one, else as "[ClassName]": a request
+ *   or socket object keeps the request headers, and with them the credentials, in fields such as _header;
+ * - a bigint, which JSON.stringify throws on, becomes its digits, and a value that cannot be read becomes "[unreadable]".
+ */
+const toLoggable = (value: unknown, options: LogFormatOptions, ancestors: object[]): unknown => {
+	if (typeof value === "bigint") return value.toString();
+	if (typeof value !== "object" || value === null) return value;
+	if (ancestors.includes(value)) return "[Circular]";
+
+	ancestors.push(value);
+	try {
+		if (value instanceof Error) {
+			const { name, message } = describeError(value);
+			return options.stack && typeof value.stack === "string" ? { name, message, stack: value.stack } : { name, message };
+		}
+		if (Array.isArray(value)) return value.map((item) => toLoggable(item, options, ancestors));
+
+		const prototype = Object.getPrototypeOf(value);
+		if (prototype !== Object.prototype && prototype !== null) {
+			const { toJSON } = value as { toJSON?: unknown };
+			if (typeof toJSON === "function") return toLoggable(toJSON.call(value), options, ancestors);
+			const name = (value as { constructor?: { name?: unknown } }).constructor?.name;
+			return `[${typeof name === "string" && name !== "" ? name : "object"}]`;
+		}
+
+		const copy: Record<string, unknown> = {};
+		for (const key of Object.keys(value)) {
+			const field = (value as Record<string, unknown>)[key];
+			// Dropped as JSON.stringify drops them; a function named toJSON would also be called on the copy.
+			if (typeof field === "function") continue;
+			copy[key] = SENSITIVE_KEY.test(key) ? REDACTED : toLoggable(field, options, ancestors);
+		}
+		return copy;
+	} catch {
+		return "[unreadable]";
+	} finally {
+		ancestors.pop();
+	}
+};
+
+const asText = (value: unknown): string => {
+	try {
+		return String(value);
+	} catch {
+		return "[unreadable]";
+	}
+};
+
+/**
+ * One console line: `<timestamp>Z <level>: <message> <all other fields as indented JSON, if any>`. Never throws: a log call that
+ * throws loses the line, and in Strapi's error middleware the error it was logging.
+ */
+export const formatLogLine = ({ timestamp, level, message, ...rest }: LogInfo, options: LogFormatOptions = {}): string => {
+	let restString = JSON.stringify(toLoggable(rest, options, []), undefined, 2);
 	restString = restString === "{}" ? "" : restString;
 
-	return `${timestamp}Z ${level}: ${message} ${restString}`;
+	return `${asText(timestamp)}Z ${asText(level)}: ${asText(message)} ${restString}`;
 };

src/services/PayPalApi.ts

@@ -1,76 +1,80 @@
-import { Client, Environment, LogLevel, OrdersController, OrderRequest } from "@paypal/paypal-server-sdk";
+import { Client, OrdersController } from "@paypal/paypal-server-sdk";
+import type { Environment, OrderRequest } from "@paypal/paypal-server-sdk";
 import { paypalClientId, paypalClientSecret, paypalEnvironment } from "../../config/constants";
-import { Order } from "../../types";
-import { buildPayPalOrderItems, buildPayPalOrderRequest } from "../checkout/paypal-order";
+import { createPayPalClient, paypalClientConfiguration } from "../checkout/paypal-client";
+import type { PayPalClient } from "../checkout/paypal-client";
+import { buildPayPalOrderRequest } from "../checkout/paypal-order";
+import type { PayPalOrderSource } from "../checkout/paypal-order";
+import { describeError } from "../logging/error";
 
 class PayPalApi {
-	private readonly client: Client;
-	private readonly ordersController: OrdersController;
+	// A new SDK Client and OrdersController after a failed token request, a network error, 401 or 5xx: see src/checkout/paypal-client.ts.
+	private readonly orders: PayPalClient<OrdersController>;
 
 	constructor(clientId: string, clientSecret: string, environment: Environment) {
-		this.client = new Client({
-			clientCredentialsAuthCredentials: {
-				oAuthClientId: clientId,
-				oAuthClientSecret: clientSecret
-			},
-			timeout: 0,
-			environment,
-			logging: {
-				logLevel: LogLevel.Info,
-				logRequest: { logBody: true },
-				logResponse: { logHeaders: true }
-			}
+		this.orders = createPayPalClient({
+			configuration: paypalClientConfiguration({ clientId, clientSecret, environment }),
+			createController: (configuration) => new OrdersController(new Client(configuration)),
+			onReplace: (error) =>
+				strapi.log.warn("app:w:paypal-api: Replacing the PayPal client after a failed request", { error: describeError(error) })
 		});
-		this.ordersController = new OrdersController(this.client);
 	}
 
-	async createSessionOrThrow(returnUrl: string, order: Order) {
-		// Outside the try block, so these throws are not logged here. The items are computed but not sent.
-		buildPayPalOrderItems(order);
+	/**
+	 * Creates the PayPal order for the order and returns PayPal's id for it, which the capture accepts, and its links. Throws
+	 * CheckoutNotReadyError or ProductUnavailableError before PayPal is asked, for an order PayPal cannot take.
+	 */
+	async createSessionOrThrow(returnUrl: string, order: PayPalOrderSource & { id?: number | string }): Promise<{ id: string; links: unknown }> {
+		// Outside the try block: an order that is not ready is the customer's to fix, not a PayPal failure.
+		const request = buildPayPalOrderRequest(returnUrl, order) as OrderRequest;
 
 		try {
-			const collect = {
-				body: buildPayPalOrderRequest(returnUrl, order) as OrderRequest,
-				prefer: "return=minimal"
-			};
+			const { body } = await this.orders.call((orders) => orders.ordersCreate({ body: request, prefer: "return=minimal" }));
+			const session = JSON.parse(body as string);
+			if (typeof session?.id !== "string" || session.id === "") throw new Error("PayPal answered without an order id");
 
-			strapi.log.silly("app:d:paypal-api: Creating PayPal order " + JSON.stringify({ collect }));
-
-			const { body, ...httpResponse } = await this.ordersController.ordersCreate(collect);
-			const sessionData = JSON.parse(body as string);
-
-			strapi.log.info("app:i:paypal-api: " + JSON.stringify({ session: sessionData }));
-
-			return {
-				id: sessionData.id,
-				links: sessionData.links
-			};
+			// The PayPal order's id and status only: the request and PayPal's order hold the buyer's name and address.
+			strapi.log.info("app:i:paypal-api: Created the PayPal order", {
+				order: order.id,
+				paypalOrderId: session.id,
+				status: typeof session.status === "string" ? session.status : undefined
+			});
+			return { id: session.id, links: session.links };
 		} catch (error) {
-			strapi.log.error("app:e:paypal-api: " + JSON.stringify({ error }));
+			// Never the error object: an SDK or axios error carries the request with its Authorization header.
+			strapi.log.error("app:e:paypal-api: Creating the PayPal order failed", { order: order.id, error: describeError(error) });
 			throw error;
 		}
 	}
 
-	async checkPaymentStatus(redirect: { orderID: string }) {
-		try {
-			const collect = {
-				id: redirect.orderID,
-				prefer: "return=minimal"
-			};
-
-			const { body } = await this.ordersController.ordersCapture(collect);
-			const captureResult = JSON.parse(body as string);
-			strapi.log.info("app:i:paypal-api: " + JSON.stringify({ captureResult }));
-
-			return captureResult;
-		} catch (error) {
-			return "/result/error";
-		}
+	/** PayPal's order as parsed JSON in PayPal's snake_case (GET /v2/checkout/orders/:id). Throws PayPal's and network errors. */
+	async getOrder(id: string): Promise<unknown> {
+		const { body } = await this.orders.call((orders) => orders.ordersGet({ id }));
+		return JSON.parse(body as string);
 	}
 
-	async handleWebhook(req: any) {
-		// Implement PayPal webhook validation and processing
-		strapi.log.verbose("app:i:paypal-api: " + JSON.stringify({ req }));
+	/**
+	 * Captures the PayPal order and returns the whole order after the capture as parsed JSON in PayPal's snake_case
+	 * (POST /v2/checkout/orders/:id/capture, Prefer: return=representation). PayPal answers a repeated requestId with the
+	 * response of the first capture instead of capturing again. Throws PayPal's and network errors.
+	 */
+	async captureOrder(id: string, requestId: string): Promise<unknown> {
+		const { body } = await this.orders.call((orders) =>
+			orders.ordersCapture({ id, paypalRequestId: requestId, prefer: "return=representation" })
+		);
+		return JSON.parse(body as string);
+	}
+
+	async handleWebhook(req: unknown) {
+		// Implement PayPal webhook validation and processing. The event's resource holds the buyer's name and address, so only the
+		// event type and the resource's id and status are logged.
+		const event = (typeof req === "object" && req !== null ? req : {}) as { event_type?: unknown; resource?: { id?: unknown; status?: unknown } };
+		const textOf = (value: unknown) => (typeof value === "string" ? value : undefined);
+		strapi.log.verbose("app:v:paypal-api: Webhook received", {
+			eventType: textOf(event.event_type),
+			resource: textOf(event.resource?.id),
+			status: textOf(event.resource?.status)
+		});
 
 		// Note: PayPal webhook handling requires specific implementation
 		// This is a placeholder and should be replaced with actual PayPal webhook validation

tests/unit/capture-payment.test.ts

@@ -0,0 +1,375 @@
+import { test } from "node:test";
+import assert from "node:assert/strict";
+import { readFileSync } from "node:fs";
+import {
+	ALREADY_PAID,
+	NOT_CONFIRMED,
+	NOT_FOUND,
+	NOT_MATCHING,
+	NOT_RECORDED,
+	NOT_THIS_ORDER,
+	ORDER_CHANGED,
+	PAYPAL_FAILED,
+	capturePayment,
+	captureRequestId
+} from "../../src/checkout/capture-payment.ts";
+import { formatLogLine } from "../../src/logging/format.ts";
+
+const UUID = "11111111-2222-4333-8444-555555555555";
+const PAYPAL_ORDER_ID = "5O190127TN364715T";
+const OTHER_PAYPAL_ORDER_ID = "8MC585209K746392H";
+const CAPTURE_ID = "3C679366HH908993F";
+// The server's time when the capture request arrives.
+const NOW = new Date("2026-10-08T19:13:05.000Z");
+const CREDENTIALS = "RFVNTVlfQ0xJRU5UX0lEOkRVTU1ZX0NMSUVOVF9TRUNSRVQ="; // base64 of the dummy "DUMMY_CLIENT_ID:DUMMY_CLIENT_SECRET"
+
+// PayPal's Orders v2 JSON for the order below, see paypal-verify.test.ts. Every call returns a fresh copy to change.
+const fixture = (name: string) => JSON.parse(readFileSync(new URL(`./fixtures/${name}`, import.meta.url), "utf8"));
+
+// The row the capture reads with strapi.db.query("api::order.order").findOne({ where: { uuid } }) after a checkout stored the
+// PayPal order it created: subtotal 17.90, delivery 4.95, total 22.85.
+const orderRow = (overrides = {}) => ({
+	id: 4711,
+	uuid: UUID,
+	email: "erika@example.org",
+	subtotal: 17.9,
+	total: 22.85,
+	VAT: 2.86,
+	paymentAuthorised: false,
+	paymentStatus: null,
+	invoiceSent: false,
+	paypalOrderId: PAYPAL_ORDER_ID,
+	paypalCaptureId: null,
+	paymentCapturedAt: null,
+	...overrides
+});
+
+/**
+ * Fakes of the dependencies over one order row, which record every call and every log line. updateOrder writes like the
+ * controller's update with where { id, paypalOrderId }: only while the row still carries that PayPal order, else it answers null.
+ * duringCapture runs while PayPal captures, as a request that changes the order at that moment would.
+ */
+const setup = ({
+	row = orderRow(),
+	paypalOrder = fixture("paypal-order-approved.json"),
+	captured = fixture("paypal-order-captured.json"),
+	getError = undefined,
+	captureError = undefined,
+	updateError = undefined,
+	duringCapture = (row) => {}
+} = {}) => {
+	const calls = { findOrder: [], getPayPalOrder: [], capturePayPalOrder: [], updateOrder: [] };
+	const logs = [];
+	const deps = {
+		findOrder: async (uuid) => {
+			calls.findOrder.push(uuid);
+			return row !== null && row.uuid === uuid ? { ...row } : null;
+		},
+		getPayPalOrder: async (id) => {
+			calls.getPayPalOrder.push(id);
+			if (getError) throw getError;
+			return paypalOrder;
+		},
+		capturePayPalOrder: async (id, requestId) => {
+			calls.capturePayPalOrder.push({ id, requestId });
+			duringCapture(row);
+			if (captureError) throw captureError;
+			return captured;
+		},
+		updateOrder: async (id, paypalOrderId, data) => {
+			calls.updateOrder.push({ id, paypalOrderId, data });
+			if (updateError) throw updateError;
+			if (row.id !== id || row.paypalOrderId !== paypalOrderId) return null;
+			Object.assign(row, data);
+			return { ...row };
+		},
+		log: {
+			info: (message, fields) => logs.push({ level: "info", message, fields }),
+			warn: (message, fields) => logs.push({ level: "warn", message, fields }),
+			error: (message, fields) => logs.push({ level: "error", message, fields })
+		}
+	};
+	return { deps, calls, logs, row };
+};
+
+const capture = (deps, { uuid = UUID, paypalOrderId = PAYPAL_ORDER_ID } = {}) => capturePayment(deps, { uuid, paypalOrderId, now: NOW });
+
+const paypalCalls = (calls) => calls.getPayPalOrder.length + calls.capturePayPalOrder.length;
+
+// What must never reach the log: the credentials of a failed request, and the buyer's data in PayPal's responses.
+const NEVER_LOGGED = [CREDENTIALS, "Authorization", "Erika", "Mustermann", "erika", "Musterstraße", "QYR5Z8XDVJNXQ", "INSTRUMENT_DECLINED"];
+
+/** Checks the recorded log, and each line as the console shows it (config/logger.ts formats with formatLogLine). */
+const assertCleanLog = (logs) => {
+	const lines = logs.map(({ level, message, fields }) =>
+		formatLogLine({ timestamp: "2026-10-08 19:13:05.000", level, message: `app:${level[0]}:order-controller: ${message}`, ...fields })
+	);
+	for (const text of [JSON.stringify(logs), ...lines]) {
+		for (const value of NEVER_LOGGED) assert.ok(!text.includes(value), `the log holds ${value}: ${text}`);
+	}
+};
+
+// What the PayPal SDK throws for an error response: @apimatic/core's ApiError, here the SDK's CustomError, with the request, whose
+// Authorization header holds the client credentials (token request) or an access token, and PayPal's error body.
+const paypalApiError = (statusCode: number, message: string) =>
+	Object.assign(new Error(message), {
+		request: {
+			method: "POST",
+			url: `https://api-m.sandbox.paypal.com/v2/checkout/orders/${PAYPAL_ORDER_ID}/capture`,
+			headers: { Authorization: `Basic ${CREDENTIALS}`, "PayPal-Request-Id": captureRequestId(UUID, PAYPAL_ORDER_ID) }
+		},
+		statusCode,
+		headers: { "paypal-debug-id": "f1a2b3c4d5e6f" },
+		body: JSON.stringify({ name: "UNPROCESSABLE_ENTITY", details: [{ issue: "INSTRUMENT_DECLINED" }], debug_id: "f1a2b3c4d5e6f" })
+	});
+
+// What axios throws when PayPal cannot be reached: the request config with its headers.
+const networkError = (message = "getaddrinfo EAI_AGAIN api-m.sandbox.paypal.com") =>
+	Object.assign(new Error(message), {
+		name: "AxiosError",
+		code: "EAI_AGAIN",
+		config: { method: "post", url: "https://api-m.sandbox.paypal.com/v1/oauth2/token", headers: { Authorization: `Basic ${CREDENTIALS}` } }
+	});
+
+// The capture
+
+test("captures the PayPal order the checkout stored and writes exactly the payment fields", async () => {
+	const { deps, calls, logs } = setup();
+	const result = await capture(deps);
+
+	assert.equal(result.status, 200);
+	assert.equal(result.alreadyCaptured, false);
+	assert.deepEqual(calls.findOrder, [UUID]);
+	assert.deepEqual(calls.getPayPalOrder, [PAYPAL_ORDER_ID]);
+	assert.deepEqual(calls.capturePayPalOrder, [{ id: PAYPAL_ORDER_ID, requestId: `capture-${UUID}-${PAYPAL_ORDER_ID}` }]);
+	assert.deepEqual(calls.updateOrder, [
+		{
+			id: 4711,
+			paypalOrderId: PAYPAL_ORDER_ID,
+			data: { paymentAuthorised: true, paymentStatus: "captured", paypalCaptureId: CAPTURE_ID, paymentCapturedAt: "2026-10-08T19:13:05.000Z" }
+		}
+	]);
+	// the controller answers the updated order, sanitized
+	assert.equal(result.order.paymentAuthorised, true);
+	assert.deepEqual(logs, [{ level: "info", message: "Captured the payment", fields: { order: 4711, capture: CAPTURE_ID } }]);
+	assertCleanLog(logs);
+});
+
+test("sends the same PayPal-Request-Id on every attempt, so that PayPal captures once", async () => {
+	assert.equal(captureRequestId(UUID, PAYPAL_ORDER_ID), "capture-11111111-2222-4333-8444-555555555555-5O190127TN364715T");
+	// PayPal accepts at most 108 characters
+	assert.ok(captureRequestId(UUID, PAYPAL_ORDER_ID).length <= 108);
+
+	// The first attempt times out after PayPal may have captured. The retry repeats the id, and PayPal answers the first capture.
+	const first = setup({ captureError: Object.assign(networkError("timeout of 30000ms exceeded"), { code: "ECONNABORTED" }) });
+	assert.deepEqual(await capture(first.deps), { status: 502, message: PAYPAL_FAILED });
+	const retry = setup();
+	assert.equal((await capture(retry.deps)).status, 200);
+
+	assert.equal(first.calls.capturePayPalOrder[0].requestId, retry.calls.capturePayPalOrder[0].requestId);
+});
+
+// Paying a cheap order, capturing an expensive one
+
+test("rejects a PayPal order the checkout did not store on the order, without asking PayPal", async () => {
+	// The buyer paid order A with PayPal order OTHER_PAYPAL_ORDER_ID and calls the capture of the expensive order B with it.
+	const { deps, calls, logs, row } = setup({ row: orderRow({ id: 4712, uuid: UUID, total: 249 }) });
+
+	assert.deepEqual(await capture(deps, { paypalOrderId: OTHER_PAYPAL_ORDER_ID }), { status: 409, message: NOT_THIS_ORDER });
+	assert.equal(paypalCalls(calls), 0);
+	assert.equal(calls.updateOrder.length, 0);
+	assert.equal(row.paymentAuthorised, false);
+	assert.deepEqual(logs, [
+		{
+			level: "warn",
+			message: "Rejected a capture with a PayPal order the checkout did not create for the order",
+			fields: { order: 4712, hasPayPalOrder: true }
+		}
+	]);
+});
+
+test("rejects every PayPal order for an order without a stored one, without asking PayPal", async () => {
+	// no checkout yet, an order from before the checkout stored it, or a cart changed since the checkout
+	for (const paypalOrderId of [null, undefined, ""]) {
+		const { deps, calls, logs } = setup({ row: orderRow({ paypalOrderId }) });
+
+		assert.deepEqual(await capture(deps), { status: 409, message: NOT_THIS_ORDER });
+		assert.equal(paypalCalls(calls) + calls.updateOrder.length, 0);
+		assert.equal(logs[0].fields.hasPayPalOrder, false);
+	}
+
+	// a request without a PayPal order id
+	const { deps, calls } = setup();
+	assert.deepEqual(await capture(deps, { paypalOrderId: "" }), { status: 409, message: NOT_THIS_ORDER });
+	assert.equal(paypalCalls(calls), 0);
+});
+
+test("does not capture a PayPal order whose amount is not the order total", async () => {
+	const paypalOrder = fixture("paypal-order-approved.json");
+	paypalOrder.purchase_units[0].amount.value = "2.29";
+	const { deps, calls, logs } = setup({ paypalOrder });
+
+	assert.deepEqual(await capture(deps), { status: 409, message: NOT_MATCHING });
+	assert.deepEqual(calls.getPayPalOrder, [PAYPAL_ORDER_ID]);
+	assert.equal(calls.capturePayPalOrder.length, 0);
+	assert.equal(calls.updateOrder.length, 0);
+	assert.deepEqual(logs, [
+		{
+			level: "warn",
+			message: "Rejected a capture: the PayPal order does not match the order",
+			fields: { order: 4711, reason: "the PayPal order amount 2.29 is not the order total 22.85" }
+		}
+	]);
+	assertCleanLog(logs);
+});
+
+test("does not capture a PayPal order created for another order, in another currency or not approved", async () => {
+	const cases: [(paypalOrder) => void, string][] = [
+		[
+			(paypalOrder) => (paypalOrder.purchase_units[0].custom_id = "99999999-8888-4777-8666-555555555555"),
+			"the custom_id of the PayPal order is not the order's uuid"
+		],
+		[(paypalOrder) => (paypalOrder.purchase_units[0].amount.currency_code = "USD"), "the PayPal order currency is USD, not EUR"],
+		[(paypalOrder) => (paypalOrder.status = "CREATED"), "the PayPal order status is CREATED, not APPROVED"]
+	];
+	for (const [change, reason] of cases) {
+		const paypalOrder = fixture("paypal-order-approved.json");
+		change(paypalOrder);
+		const { deps, calls, logs } = setup({ paypalOrder });
+
+		assert.deepEqual(await capture(deps), { status: 409, message: NOT_MATCHING });
+		assert.equal(calls.capturePayPalOrder.length + calls.updateOrder.length, 0);
+		assert.equal(logs[0].fields.reason, reason);
+		assertCleanLog(logs);
+	}
+});
+
+// A paid order
+
+test("answers alreadyCaptured for a paid order and the PayPal order it was paid with, without a call or a write", async () => {
+	const { deps, calls, logs } = setup({ row: orderRow({ paymentAuthorised: true, paymentStatus: "captured", paypalCaptureId: CAPTURE_ID }) });
+
+	assert.deepEqual(await capture(deps), { status: 200, alreadyCaptured: true });
+	assert.equal(paypalCalls(calls) + calls.updateOrder.length, 0);
+	assert.deepEqual(logs, []);
+});
+
+test("rejects another PayPal order for a paid order, without a call or a write", async () => {
+	const paidRows = [
+		orderRow({ paymentAuthorised: true, paymentStatus: "captured", paypalCaptureId: CAPTURE_ID }),
+		// paid before the checkout stored the PayPal order
+		orderRow({ paymentAuthorised: true, paymentStatus: "authorised", paypalOrderId: null })
+	];
+	for (const row of paidRows) {
+		const { deps, calls } = setup({ row });
+
+		assert.deepEqual(await capture(deps, { paypalOrderId: OTHER_PAYPAL_ORDER_ID }), { status: 409, message: ALREADY_PAID });
+		assert.equal(paypalCalls(calls) + calls.updateOrder.length, 0);
+	}
+});
+
+test("answers 404 for a missing order, without asking PayPal", async () => {
+	const { deps, calls } = setup({ row: null });
+
+	assert.deepEqual(await capture(deps), { status: 404, message: NOT_FOUND });
+	assert.equal(paypalCalls(calls), 0);
+
+	// No uuid: no lookup at all, since Strapi drops an undefined where condition and would find any order.
+	for (const uuid of ["", undefined]) {
+		const { deps, calls } = setup();
+		assert.deepEqual(await capturePayment(deps, { uuid, paypalOrderId: PAYPAL_ORDER_ID, now: NOW }), { status: 404, message: NOT_FOUND });
+		assert.deepEqual(calls.findOrder, []);
+	}
+});
+
+// PayPal fails
+
+test("answers 502 when PayPal fails, and logs the error's name, message and status code but not its request", async () => {
+	const failures: [string, Error & { statusCode?: number }][] = [
+		["getError", paypalApiError(401, "Authentication failed due to missing authorization header, or invalid authentication credentials.")],
+		["getError", networkError()],
+		["captureError", paypalApiError(422, "The requested action could not be performed, semantically incorrect, or failed business validation.")],
+		["captureError", networkError()]
+	];
+	for (const [failing, error] of failures) {
+		const { deps, calls, logs, row } = setup({ [failing]: error });
+
+		assert.deepEqual(await capture(deps), { status: 502, message: PAYPAL_FAILED });
+		assert.equal(calls.capturePayPalOrder.length, failing === "getError" ? 0 : 1);
+		assert.equal(calls.updateOrder.length, 0);
+		assert.equal(row.paymentAuthorised, false);
+		assert.equal(logs.length, 1);
+		assert.equal(logs[0].level, "error");
+		assert.deepEqual(logs[0].fields, { order: 4711, error: { name: error.name, message: error.message, statusCode: error.statusCode } });
+		assertCleanLog(logs);
+	}
+});
+
+// After PayPal answered the capture
+
+test("keeps the order unpaid and answers 502 when the capture does not match, logging the order and the reason only", async () => {
+	const pending = fixture("paypal-order-captured.json");
+	pending.purchase_units[0].payments.captures[0].status = "PENDING";
+	const lower = fixture("paypal-order-captured.json");
+	lower.purchase_units[0].payments.captures[0].amount.value = "2.29";
+	const minimal = { id: PAYPAL_ORDER_ID, status: "COMPLETED", links: [] };
+
+	const cases: [unknown, string][] = [
+		[pending, "the capture status is PENDING, not COMPLETED"],
+		[lower, "the capture amount 2.29 is not the order total 22.85"],
+		[minimal, "the capture response has no capture"]
+	];
+	for (const [captured, reason] of cases) {
+		const { deps, calls, logs, row } = setup({ captured });
+
+		assert.deepEqual(await capture(deps), { status: 502, message: NOT_CONFIRMED });
+		assert.equal(calls.updateOrder.length, 0);
+		assert.equal(row.paymentAuthorised, false);
+		assert.deepEqual(logs, [
+			{
+				level: "error",
+				message: "The PayPal capture does not match the order, which stays unpaid: check the PayPal order for a refund",
+				fields: { order: 4711, reason }
+			}
+		]);
+		assertCleanLog(logs);
+	}
+});
+
+test("keeps the order unpaid when its cart or address changed during the capture", async () => {
+	// addProduct, removeProduct and updateByUuid clear paypalOrderId in the write that changes the order
+	const { deps, calls, logs, row } = setup({
+		duringCapture: (row) => {
+			row.total = 249;
+			row.paypalOrderId = null;
+		}
+	});
+
+	assert.deepEqual(await capture(deps), { status: 409, message: ORDER_CHANGED });
+	assert.equal(calls.updateOrder.length, 1);
+	assert.equal(row.paymentAuthorised, false);
+	assert.deepEqual(logs, [
+		{
+			level: "error",
+			message: "PayPal captured the payment, but the order changed during the capture and stays unpaid: check the order for a refund",
+			fields: { order: 4711, capture: CAPTURE_ID }
+		}
+	]);
+});
+
+test("answers 500 when the order cannot be marked paid after the capture, and logs the capture", async () => {
+	const { deps, logs } = setup({ updateError: new Error("Connection terminated unexpectedly") });
+
+	assert.deepEqual(await capture(deps), { status: 500, message: NOT_RECORDED });
+	assert.deepEqual(logs, [
+		{
+			level: "error",
+			message: "PayPal captured the payment, but the order could not be marked paid: check the order",
+			fields: {
+				order: 4711,
+				capture: CAPTURE_ID,
+				error: { name: "Error", message: "Connection terminated unexpectedly", statusCode: undefined }
+			}
+		}
+	]);
+});

tests/unit/customer-update.test.ts

@@ -0,0 +1,351 @@
+import { test } from "node:test";
+import assert from "node:assert/strict";
+import { parseCustomerUpdate } from "../../src/checkout/customer-update.ts";
+
+// The server's time when the update arrives.
+const NOW = new Date("2026-10-08T19:12:05.000Z");
+
+const parse = (body: unknown) => parseCustomerUpdate(body, NOW);
+
+// The names of the fields a body is rejected for, or [] if it is accepted.
+const rejectedFields = (body: unknown) => {
+	const result = parse(body);
+	return result.ok ? [] : result.fields;
+};
+
+// What the controller receives: the JSON the shop sent, parsed by Strapi's body parser.
+const wire = (body: unknown) => JSON.parse(JSON.stringify(body));
+
+// The shop's checkout, libreshop/shop: useCart().update(data) sends { data } (composables/useShopApi.ts, updateOrder), and its
+// server route forwards that body unchanged.
+// Step 1, pages/checkout/1.vue: the email and the time the browser thinks the terms were accepted.
+const STEP_1 = { data: { email: "erika@example.org", acceptedTermsAndConditionsAt: "2026-10-08T19:12:03.512Z" } };
+
+// Step 2, pages/checkout/2.vue: addressToString and mapToStructuredAddress of the form, and the id of the chosen delivery method.
+// Without a different delivery address, the delivery address is the invoice address.
+const ERIKA = {
+	givenName: "Erika",
+	familyName: "Mustermann",
+	streetAddress: "Musterstraße 1",
+	postalCode: "70190",
+	addressLevel2: "Stuttgart",
+	country: "DE"
+};
+const ERIKA_TEXT = "Erika Mustermann\nMusterstraße 1\n70190 Stuttgart";
+const STEP_2 = {
+	data: { invoiceAddress: ERIKA_TEXT, deliveryAddress: ERIKA_TEXT, invoiceAddressStructured: ERIKA, deliveryAddressStructured: ERIKA, delivery: 1 }
+};
+
+const MAX = {
+	givenName: "Max",
+	familyName: "Mustermann",
+	streetAddress: "Hauptstraße 5",
+	postalCode: "10115",
+	addressLevel2: "Berlin",
+	country: "DE"
+};
+const MAX_TEXT = "Max Mustermann\nHauptstraße 5\n10115 Berlin";
+
+// Every attribute of the order that only the server writes (src/api/order/content-types/order/schema.json), among them the PayPal
+// order the checkout stores and the capture it verified, and the fields Strapi manages; with values a client would send to get a
+// paid order for less.
+const SERVER_FIELDS = {
+	paymentAuthorised: true,
+	paymentStatus: "captured",
+	paypalOrderId: "5O190127TN364715T",
+	paypalCaptureId: "3C679366HH908993F",
+	paymentCapturedAt: "2026-01-01T00:00:00.000Z",
+	total: 0.01,
+	subtotal: 0.01,
+	VAT: 0,
+	invoiceNumber: "R-1-1",
+	invoice: 1,
+	invoiceSent: false,
+	deliveryNote: 1,
+	deliveryNoteNumber: "L-1-1",
+	deliveryNoteSent: true,
+	deliveryTrackingNumber: "00340434161094042557",
+	emailSent: true,
+	cart: [{ product: 101, count: 100 }],
+	customer: 1,
+	payment: 1,
+	uuid: "11111111-2222-4333-8444-555555555555",
+	hash: "0",
+	date: "2026-01-01",
+	id: 1,
+	createdAt: "2026-01-01T00:00:00.000Z",
+	updatedAt: "2026-01-01T00:00:00.000Z",
+	publishedAt: "2026-01-01T00:00:00.000Z",
+	createdBy: 1,
+	updatedBy: 1
+};
+
+// What the shop sends
+
+test("accepts the shop's step 1 payload: the email, and the terms accepted at the server's time", (t) => {
+	const result = parse(wire(STEP_1));
+	t.diagnostic(`output: ${JSON.stringify(result)}`);
+
+	assert.deepEqual(result, { ok: true, data: { email: "erika@example.org", acceptedTermsAndConditionsAt: "2026-10-08T19:12:05.000Z" } });
+});
+
+test("accepts the shop's step 2 payload: both addresses as text and structured, and the delivery method", (t) => {
+	const result = parse(wire(STEP_2));
+	t.diagnostic(`output: ${JSON.stringify(result)}`);
+
+	assert.deepEqual(result, {
+		ok: true,
+		data: {
+			invoiceAddress: ERIKA_TEXT,
+			deliveryAddress: ERIKA_TEXT,
+			invoiceAddressStructured: ERIKA,
+			deliveryAddressStructured: ERIKA,
+			delivery: 1
+		}
+	});
+});
+
+test("accepts the shop's step 2 payload with a different delivery address", () => {
+	const body = { data: { ...STEP_2.data, deliveryAddress: MAX_TEXT, deliveryAddressStructured: MAX, delivery: 2 } };
+
+	assert.deepEqual(parse(wire(body)), { ok: true, data: body.data });
+});
+
+// What only the server writes
+
+for (const [field, value] of Object.entries(SERVER_FIELDS)) {
+	test(`rejects ${field}, which only the server writes`, () => {
+		assert.deepEqual(parse({ data: { [field]: value } }), {
+			ok: false,
+			errors: [`data.${field}: not a field the customer may set`],
+			fields: [`data.${field}`]
+		});
+	});
+}
+
+test("rejects the whole update, not just the server-only fields, when they come with the shop's fields", () => {
+	assert.deepEqual(parse({ data: { ...STEP_1.data, paymentAuthorised: true, paymentStatus: "authorised" } }), {
+		ok: false,
+		errors: ["data.paymentAuthorised: not a field the customer may set", "data.paymentStatus: not a field the customer may set"],
+		fields: ["data.paymentAuthorised", "data.paymentStatus"]
+	});
+});
+
+test("names the rejected fields but never repeats their values", () => {
+	const result = parse({
+		data: {
+			email: "SECRET erika@example.org",
+			invoiceAddress: { SECRET: true },
+			invoiceAddressStructured: { ...ERIKA, givenName: "SECRET".repeat(40) },
+			invoiceNumber: "R-SECRET",
+			delivery: "SECRET"
+		}
+	});
+
+	assert.equal(result.ok, false);
+	assert.deepEqual(result.ok ? [] : result.fields, [
+		"data.email",
+		"data.invoiceAddress",
+		"data.invoiceAddressStructured.givenName",
+		"data.invoiceNumber",
+		"data.delivery"
+	]);
+	assert.ok(!JSON.stringify(result).includes("SECRET"), JSON.stringify(result));
+});
+
+// The terms
+
+test("records the server's time as the time the terms were accepted, whatever the client sends", () => {
+	for (const sent of ["2026-10-08T19:12:03.512Z", "1999-12-31T23:00:00.000Z", "2030-01-01T00:00:00.000Z", "yes", true, 1]) {
+		assert.deepEqual(parse({ data: { acceptedTermsAndConditionsAt: sent } }), {
+			ok: true,
+			data: { acceptedTermsAndConditionsAt: "2026-10-08T19:12:05.000Z" }
+		});
+	}
+
+	assert.deepEqual(parseCustomerUpdate({ data: { acceptedTermsAndConditionsAt: true } }, new Date("2026-10-09T06:30:00.000Z")), {
+		ok: true,
+		data: { acceptedTermsAndConditionsAt: "2026-10-09T06:30:00.000Z" }
+	});
+});
+
+test("rejects a terms acceptance without a true value", () => {
+	for (const sent of [false, null, "", 0]) {
+		assert.deepEqual(parse({ data: { acceptedTermsAndConditionsAt: sent } }), {
+			ok: false,
+			errors: ["data.acceptedTermsAndConditionsAt: must be sent only to accept the terms, as true or a timestamp"],
+			fields: ["data.acceptedTermsAndConditionsAt"]
+		});
+	}
+});
+
+// The email
+
+test("accepts an email address trimmed, up to 254 characters", () => {
+	const longest = `${"e".repeat(242)}@example.org`;
+	assert.equal(longest.length, 254);
+
+	assert.deepEqual(parse({ data: { email: "  erika@example.org\n" } }), { ok: true, data: { email: "erika@example.org" } });
+	assert.deepEqual(parse({ data: { email: longest } }), { ok: true, data: { email: longest } });
+});
+
+test("rejects an email that is not an address of at most 254 characters", () => {
+	const emails = [
+		"",
+		"   ",
+		"erika",
+		"erika.example.org",
+		"@example.org",
+		"erika@",
+		`${"e".repeat(243)}@example.org`,
+		"erika mustermann@example.org",
+		"erika@example.org\r\nBcc: everyone@example.org",
+		"erika@exa\u0000mple.org",
+		null,
+		42,
+		true,
+		["erika@example.org"],
+		{ address: "erika@example.org" }
+	];
+	for (const email of emails) {
+		assert.deepEqual(
+			parse({ data: { email } }),
+			{ ok: false, errors: ["data.email: must be an email address of at most 254 characters"], fields: ["data.email"] },
+			JSON.stringify(email)
+		);
+	}
+});
+
+// The addresses
+
+test("accepts an invoice or delivery address of up to 500 characters", () => {
+	const longest = `${ERIKA_TEXT}\n${"c/o ".repeat(113)}`;
+	assert.equal(longest.length, 500);
+
+	assert.deepEqual(parse({ data: { invoiceAddress: longest, deliveryAddress: longest } }), {
+		ok: true,
+		data: { invoiceAddress: longest, deliveryAddress: longest }
+	});
+});
+
+test("rejects an invoice or delivery address that is not a string of at most 500 characters", () => {
+	for (const field of ["invoiceAddress", "deliveryAddress"]) {
+		for (const value of ["a".repeat(501), null, 42, true, [ERIKA_TEXT], { street: "Musterstraße 1" }]) {
+			assert.deepEqual(parse({ data: { [field]: value } }), {
+				ok: false,
+				errors: [`data.${field}: must be a string of at most 500 characters`],
+				fields: [`data.${field}`]
+			});
+		}
+	}
+});
+
+test("accepts a structured address with only some components, null for a component without a value, and 200 characters", () => {
+	const partial = { givenName: "Erika", familyName: null, postalCode: "70190", country: "DE" };
+	const longest = { ...ERIKA, streetAddress: "s".repeat(200) };
+
+	assert.deepEqual(parse({ data: { invoiceAddressStructured: partial } }), { ok: true, data: { invoiceAddressStructured: partial } });
+	assert.deepEqual(parse({ data: { deliveryAddressStructured: longest } }), { ok: true, data: { deliveryAddressStructured: longest } });
+});
+
+test("rejects a structured address with keys that are not its components, and names them", () => {
+	assert.deepEqual(parse({ data: { invoiceAddressStructured: { ...ERIKA, id: 7, street: "Musterstraße 1" } } }), {
+		ok: false,
+		errors: [
+			"data.invoiceAddressStructured.id: not a structured address field",
+			"data.invoiceAddressStructured.street: not a structured address field"
+		],
+		fields: ["data.invoiceAddressStructured.id", "data.invoiceAddressStructured.street"]
+	});
+});
+
+test("rejects a structured address that is not an object", () => {
+	for (const field of ["invoiceAddressStructured", "deliveryAddressStructured"]) {
+		for (const value of [null, ERIKA_TEXT, 42, true, [ERIKA]]) {
+			assert.deepEqual(parse({ data: { [field]: value } }), {
+				ok: false,
+				errors: [`data.${field}: must be an object`],
+				fields: [`data.${field}`]
+			});
+		}
+	}
+});
+
+test("rejects a structured address component that is not a string of at most 200 characters, or null", () => {
+	for (const value of ["s".repeat(201), 42, true, ["Erika"], { name: "Erika" }]) {
+		assert.deepEqual(parse({ data: { deliveryAddressStructured: { ...ERIKA, givenName: value } } }), {
+			ok: false,
+			errors: ["data.deliveryAddressStructured.givenName: must be a string of at most 200 characters, or null"],
+			fields: ["data.deliveryAddressStructured.givenName"]
+		});
+	}
+});
+
+// The delivery method
+
+test("accepts the id of a delivery method", () => {
+	for (const delivery of [1, 2, 2147483647]) {
+		assert.deepEqual(parse({ data: { delivery } }), { ok: true, data: { delivery } });
+	}
+});
+
+test("rejects a delivery that is not a positive integer", () => {
+	// NaN and Infinity cannot come as JSON, but the parser does not rely on that.
+	for (const delivery of [0, -1, 1.5, "1", null, true, [1], { id: 1 }, 2147483648, Number.NaN, Number.POSITIVE_INFINITY]) {
+		assert.deepEqual(parse({ data: { delivery } }), {
+			ok: false,
+			errors: ["data.delivery: must be the id of a delivery method, a positive integer"],
+			fields: ["data.delivery"]
+		});
+	}
+});
+
+// The body
+
+test("rejects a body that is not an object", () => {
+	for (const body of [undefined, null, "", "data", 42, true, [], [STEP_1]]) {
+		assert.deepEqual(parse(body), { ok: false, errors: ["body: must be an object of the form { data: { … } }"], fields: ["body"] });
+	}
+});
+
+test("rejects a body without data, and names the fields sent outside it", () => {
+	assert.deepEqual(parse({}), { ok: false, errors: ["data: missing"], fields: ["data"] });
+	assert.deepEqual(parse(STEP_1.data), {
+		ok: false,
+		errors: [
+			"email: not accepted, the fields belong in data",
+			"acceptedTermsAndConditionsAt: not accepted, the fields belong in data",
+			"data: missing"
+		],
+		fields: ["email", "acceptedTermsAndConditionsAt", "data"]
+	});
+});
+
+test("rejects data that is not an object", () => {
+	for (const data of [null, "email=erika@example.org", 42, true, [], [STEP_1.data]]) {
+		assert.deepEqual(parse({ data }), { ok: false, errors: ["data: must be an object"], fields: ["data"] });
+	}
+});
+
+test("rejects keys next to data", () => {
+	assert.deepEqual(rejectedFields({ ...STEP_1, meta: {}, paymentAuthorised: true }), ["meta", "paymentAuthorised"]);
+});
+
+test("rejects __proto__ and constructor like any other key", () => {
+	assert.deepEqual(rejectedFields(JSON.parse('{"__proto__": {"paymentAuthorised": true}, "data": {}}')), ["__proto__"]);
+	assert.deepEqual(rejectedFields(JSON.parse('{"data": {"__proto__": {"paymentAuthorised": true}, "constructor": {}}}')), [
+		"data.__proto__",
+		"data.constructor"
+	]);
+	assert.deepEqual(rejectedFields(JSON.parse('{"data": {"invoiceAddressStructured": {"__proto__": {"givenName": "Erika"}}}}')), [
+		"data.invoiceAddressStructured.__proto__"
+	]);
+});
+
+test("cuts a rejected key to 64 characters", () => {
+	assert.deepEqual(rejectedFields({ data: { ["k".repeat(10000)]: 1 } }), [`data.${"k".repeat(64)}…`]);
+});
+
+test("accepts an update without fields", () => {
+	assert.deepEqual(parse({ data: {} }), { ok: true, data: {} });
+});

tests/unit/fixtures/paypal-order-approved.json

@@ -0,0 +1,88 @@
+{
+	"id": "5O190127TN364715T",
+	"intent": "CAPTURE",
+	"status": "APPROVED",
+	"payment_source": {
+		"paypal": {
+			"email_address": "erika.buyer@example.org",
+			"account_id": "QYR5Z8XDVJNXQ",
+			"account_status": "VERIFIED",
+			"name": {
+				"given_name": "Erika",
+				"surname": "Mustermann"
+			},
+			"address": {
+				"country_code": "DE"
+			}
+		}
+	},
+	"purchase_units": [
+		{
+			"reference_id": "11111111-2222-4333-8444-555555555555",
+			"amount": {
+				"currency_code": "EUR",
+				"value": "22.85",
+				"breakdown": {
+					"item_total": {
+						"currency_code": "EUR",
+						"value": "15.04"
+					},
+					"shipping": {
+						"currency_code": "EUR",
+						"value": "4.95"
+					},
+					"tax_total": {
+						"currency_code": "EUR",
+						"value": "2.86"
+					}
+				}
+			},
+			"payee": {
+				"email_address": "merchant@example.com",
+				"merchant_id": "7KNGBPH2U58GQ"
+			},
+			"custom_id": "11111111-2222-4333-8444-555555555555",
+			"invoice_id": "R-12-4711",
+			"shipping": {
+				"name": {
+					"full_name": "Erika Mustermann"
+				},
+				"address": {
+					"address_line_1": "Musterstraße 1",
+					"admin_area_2": "Stuttgart",
+					"postal_code": "70190",
+					"country_code": "DE"
+				}
+			}
+		}
+	],
+	"payer": {
+		"name": {
+			"given_name": "Erika",
+			"surname": "Mustermann"
+		},
+		"email_address": "erika.buyer@example.org",
+		"payer_id": "QYR5Z8XDVJNXQ",
+		"address": {
+			"country_code": "DE"
+		}
+	},
+	"create_time": "2026-10-08T19:12:40Z",
+	"links": [
+		{
+			"href": "https://api.sandbox.paypal.com/v2/checkout/orders/5O190127TN364715T",
+			"rel": "self",
+			"method": "GET"
+		},
+		{
+			"href": "https://api.sandbox.paypal.com/v2/checkout/orders/5O190127TN364715T",
+			"rel": "update",
+			"method": "PATCH"
+		},
+		{
+			"href": "https://api.sandbox.paypal.com/v2/checkout/orders/5O190127TN364715T/capture",
+			"rel": "capture",
+			"method": "POST"
+		}
+	]
+}

tests/unit/fixtures/paypal-order-captured.json

@@ -0,0 +1,131 @@
+{
+	"id": "5O190127TN364715T",
+	"intent": "CAPTURE",
+	"status": "COMPLETED",
+	"payment_source": {
+		"paypal": {
+			"email_address": "erika.buyer@example.org",
+			"account_id": "QYR5Z8XDVJNXQ",
+			"account_status": "VERIFIED",
+			"name": {
+				"given_name": "Erika",
+				"surname": "Mustermann"
+			},
+			"address": {
+				"country_code": "DE"
+			}
+		}
+	},
+	"purchase_units": [
+		{
+			"reference_id": "11111111-2222-4333-8444-555555555555",
+			"amount": {
+				"currency_code": "EUR",
+				"value": "22.85",
+				"breakdown": {
+					"item_total": {
+						"currency_code": "EUR",
+						"value": "15.04"
+					},
+					"shipping": {
+						"currency_code": "EUR",
+						"value": "4.95"
+					},
+					"tax_total": {
+						"currency_code": "EUR",
+						"value": "2.86"
+					}
+				}
+			},
+			"payee": {
+				"email_address": "merchant@example.com",
+				"merchant_id": "7KNGBPH2U58GQ"
+			},
+			"custom_id": "11111111-2222-4333-8444-555555555555",
+			"invoice_id": "R-12-4711",
+			"shipping": {
+				"name": {
+					"full_name": "Erika Mustermann"
+				},
+				"address": {
+					"address_line_1": "Musterstraße 1",
+					"admin_area_2": "Stuttgart",
+					"postal_code": "70190",
+					"country_code": "DE"
+				}
+			},
+			"payments": {
+				"captures": [
+					{
+						"id": "3C679366HH908993F",
+						"status": "COMPLETED",
+						"amount": {
+							"currency_code": "EUR",
+							"value": "22.85"
+						},
+						"final_capture": true,
+						"seller_protection": {
+							"status": "ELIGIBLE",
+							"dispute_categories": ["ITEM_NOT_RECEIVED", "UNAUTHORIZED_TRANSACTION"]
+						},
+						"seller_receivable_breakdown": {
+							"gross_amount": {
+								"currency_code": "EUR",
+								"value": "22.85"
+							},
+							"paypal_fee": {
+								"currency_code": "EUR",
+								"value": "0.92"
+							},
+							"net_amount": {
+								"currency_code": "EUR",
+								"value": "21.93"
+							}
+						},
+						"custom_id": "11111111-2222-4333-8444-555555555555",
+						"invoice_id": "R-12-4711",
+						"links": [
+							{
+								"href": "https://api.sandbox.paypal.com/v2/payments/captures/3C679366HH908993F",
+								"rel": "self",
+								"method": "GET"
+							},
+							{
+								"href": "https://api.sandbox.paypal.com/v2/payments/captures/3C679366HH908993F/refund",
+								"rel": "refund",
+								"method": "POST"
+							},
+							{
+								"href": "https://api.sandbox.paypal.com/v2/checkout/orders/5O190127TN364715T",
+								"rel": "up",
+								"method": "GET"
+							}
+						],
+						"create_time": "2026-10-08T19:13:02Z",
+						"update_time": "2026-10-08T19:13:02Z"
+					}
+				]
+			}
+		}
+	],
+	"payer": {
+		"name": {
+			"given_name": "Erika",
+			"surname": "Mustermann"
+		},
+		"email_address": "erika.buyer@example.org",
+		"payer_id": "QYR5Z8XDVJNXQ",
+		"address": {
+			"country_code": "DE"
+		}
+	},
+	"create_time": "2026-10-08T19:12:40Z",
+	"update_time": "2026-10-08T19:13:02Z",
+	"links": [
+		{
+			"href": "https://api.sandbox.paypal.com/v2/checkout/orders/5O190127TN364715T",
+			"rel": "self",
+			"method": "GET"
+		}
+	]
+}

tests/unit/log-error.test.ts

@@ -0,0 +1,67 @@
+import { test } from "node:test";
+import assert from "node:assert/strict";
+import { describeError } from "../../src/logging/error.ts";
+import { formatLogLine } from "../../src/logging/format.ts";
+
+const TIMESTAMP = "2026-10-08 21:29:40.426";
+const CREDENTIALS = "RFVNTVlfQ0xJRU5UX0lEOkRVTU1ZX0NMSUVOVF9TRUNSRVQ="; // base64 of the dummy "DUMMY_CLIENT_ID:DUMMY_CLIENT_SECRET"
+
+// What axios throws when PayPal cannot be reached: the request config with its headers.
+const networkError = () =>
+	Object.assign(new Error("getaddrinfo EAI_AGAIN api-m.paypal.com"), {
+		name: "AxiosError",
+		code: "EAI_AGAIN",
+		config: { method: "post", url: "https://api-m.paypal.com/v1/oauth2/token", headers: { Authorization: `Basic ${CREDENTIALS}` } }
+	});
+
+test("keeps the name, message and status code of a PayPal SDK error, not its request, headers or body", () => {
+	// @apimatic/core's ApiError, which the SDK's CustomError and OAuthProviderError extend
+	const error = Object.assign(new Error("OAuth 2 Authorization endpoint returned error."), {
+		request: { method: "POST", url: "https://api-m.paypal.com/v1/oauth2/token", headers: { Authorization: `Basic ${CREDENTIALS}` } },
+		statusCode: 401,
+		headers: { "paypal-debug-id": "f1a2b3c4d5e6f" },
+		body: '{"error":"invalid_client","error_description":"Client Authentication failed"}'
+	});
+
+	assert.deepEqual(describeError(error), { name: "Error", message: "OAuth 2 Authorization endpoint returned error.", statusCode: 401 });
+});
+
+test("keeps the name and message of an axios network error, not its config", () => {
+	assert.deepEqual(describeError(networkError()), { name: "AxiosError", message: "getaddrinfo EAI_AGAIN api-m.paypal.com", statusCode: undefined });
+});
+
+test("keeps the first line of a message: the SDK's response validation error quotes the response after it", () => {
+	const error = new Error(
+		'The response did not match the response schema.\n\n> Issue #1\n\nExpected value to be of type \'string\'.\n\nGiven value: {"email_address":"erika.buyer@example.org"}'
+	);
+
+	assert.deepEqual(describeError(error), { name: "Error", message: "The response did not match the response schema.", statusCode: undefined });
+});
+
+test("cuts a long message", () => {
+	assert.equal(describeError(new Error("x".repeat(500))).message, `${"x".repeat(200)}…`);
+});
+
+test("describes a thrown value that is not an error by its type alone", () => {
+	assert.deepEqual(describeError("/result/error"), { name: "string", message: "", statusCode: undefined });
+	assert.deepEqual(describeError(undefined), { name: "undefined", message: "", statusCode: undefined });
+	assert.deepEqual(describeError(null), { name: "object", message: "", statusCode: undefined });
+	assert.deepEqual(describeError({ statusCode: "500" }), { name: "object", message: "", statusCode: undefined });
+});
+
+test("the log line of the description holds no credentials", () => {
+	// The formatter now also keeps them out of the line of the error object itself, see log-format.test.ts.
+	const line = formatLogLine({
+		timestamp: TIMESTAMP,
+		level: "error",
+		message: "app:e:order-controller: PayPal did not capture the payment",
+		order: 4711,
+		error: describeError(networkError())
+	});
+
+	assert.equal(
+		line,
+		'2026-10-08 21:29:40.426Z error: app:e:order-controller: PayPal did not capture the payment {\n  "order": 4711,\n  "error": {\n    "name": "AxiosError",\n    "message": "getaddrinfo EAI_AGAIN api-m.paypal.com"\n  }\n}'
+	);
+	assert.ok(!line.includes(CREDENTIALS));
+});

tests/unit/log-format.test.ts

@@ -33,23 +33,16 @@ test("ignores the symbol keys winston adds", () => {
 	assert.equal(formatLogLine(info), "2026-10-08 21:29:40.426Z info: hello ");
 });
 
-// Known defects: these assert the correct behaviour and fail today, which the todo marks as expected.
+// Fixed defects of https://git.librete.ch/libretech/mp/issues/67.
 
-test(
-	"does not throw on a circular reference",
-	{ todo: "JSON.stringify throws on a circular reference — https://git.librete.ch/libretech/mp/issues/67" },
-	() => {
+test("does not throw on a circular reference", () => {
 	const request: Record<string, unknown> = { method: "POST", path: "/v1/oauth2/token" };
 	request.self = request;
 
 	assert.doesNotThrow(() => formatLogLine({ timestamp: TIMESTAMP, level: "error", message: "app:e:paypal-api", request }));
-	}
-);
+});
 
-test(
-	"does not write the Authorization header of an axios-like error into the line",
-	{ todo: "the PayPal client credentials are logged — https://git.librete.ch/libretech/mp/issues/67" },
-	() => {
+test("does not write the Authorization header of an axios-like error into the line", () => {
 	const error = Object.assign(new Error("getaddrinfo EAI_AGAIN api-m.paypal.com"), {
 		name: "AxiosError",
 		code: "EAI_AGAIN",
@@ -59,13 +52,9 @@ test(
 	const line = formatLogLine({ ...error, message: `${error.message}\n${error.stack}`, level: "error", timestamp: TIMESTAMP });
 
 	assert.ok(!line.includes(CREDENTIALS), line);
-	}
-);
+});
 
-test(
-	"renders an Error with its message instead of {}",
-	{ todo: "an Error is rendered as {} — https://git.librete.ch/libretech/mp/issues/67" },
-	() => {
+test("renders an Error with its message instead of {}", () => {
 	const error = new Error("getaddrinfo EAI_AGAIN api-m.paypal.com");
 	// strapi.log.error("…", { error }), as in the order controller's capturePayment
 	const line = formatLogLine({
@@ -76,5 +65,109 @@ test(
 	});
 
 	assert.ok(line.includes("getaddrinfo EAI_AGAIN api-m.paypal.com"), line);
+});
+
+// Safe serialisation.
+
+const fieldsOf = (line: string) => JSON.parse(line.slice(line.indexOf("{")));
+
+test("redacts the fields named like a credential at any depth, whatever their case", () => {
+	const line = formatLogLine({
+		timestamp: TIMESTAMP,
+		level: "debug",
+		message: "app:d:test",
+		token: "A21AAF…",
+		request: {
+			method: "POST",
+			headers: { Authorization: `Basic ${CREDENTIALS}`, Cookie: "koa.sess=abc", "X-API-Key": "k1", "Content-Type": "application/json" },
+			body: { grant_type: "client_credentials", client_secret: "s3cr3t", user: { password: "hunter2", api_key: "k2", apikey: "k3" } },
+			responses: [{ headers: { "set-cookie": ["koa.sess=def"] }, data: { access_token: "A21AAG…", expires_in: 32400 } }]
 		}
-);
+	});
+
+	assert.deepEqual(fieldsOf(line), {
+		token: "[redacted]",
+		request: {
+			method: "POST",
+			headers: { Authorization: "[redacted]", Cookie: "[redacted]", "X-API-Key": "[redacted]", "Content-Type": "application/json" },
+			body: {
+				grant_type: "client_credentials",
+				client_secret: "[redacted]",
+				user: { password: "[redacted]", api_key: "[redacted]", apikey: "[redacted]" }
+			},
+			responses: [{ headers: { "set-cookie": "[redacted]" }, data: { access_token: "[redacted]", expires_in: 32400 } }]
+		}
+	});
+});
+
+test("writes the other fields of an object that contains itself, and the reference to it as [Circular]", () => {
+	const request: Record<string, unknown> = { method: "POST", path: "/v1/oauth2/token" };
+	request.socket = { request, remoteAddress: "151.101.1.21" };
+	const line = formatLogLine({ timestamp: TIMESTAMP, level: "error", message: "app:e:paypal-api", request, list: [request] });
+
+	assert.deepEqual(fieldsOf(line), {
+		request: { method: "POST", path: "/v1/oauth2/token", socket: { request: "[Circular]", remoteAddress: "151.101.1.21" } },
+		list: [{ method: "POST", path: "/v1/oauth2/token", socket: { request: "[Circular]", remoteAddress: "151.101.1.21" } }]
+	});
+});
+
+test("writes an object that is referenced twice, but not by itself, both times", () => {
+	const delivery = { id: 1, price: 4.95 };
+
+	assert.deepEqual(fieldsOf(formatLogLine({ timestamp: TIMESTAMP, level: "info", message: "m", before: delivery, after: delivery })), {
+		before: { id: 1, price: 4.95 },
+		after: { id: 1, price: 4.95 }
+	});
+});
+
+test("writes an Error as its name and the first line of its message, and its stack only when asked", () => {
+	const error = Object.assign(new Error('The response did not match the response schema.\n\nGiven value: {"email_address":"erika@example.org"}'), {
+		request: { url: "https://api-m.paypal.com/v2/checkout/orders", headers: { Authorization: "Bearer A21AAF…" } },
+		statusCode: 201
+	});
+	const info = { timestamp: TIMESTAMP, level: "error", message: "app:e:paypal-api", error };
+
+	assert.deepEqual(fieldsOf(formatLogLine(info)), { error: { name: "Error", message: "The response did not match the response schema." } });
+	const withStack = fieldsOf(formatLogLine(info, { stack: true }));
+	assert.equal(withStack.error.stack, error.stack);
+	assert.deepEqual(Object.keys(withStack.error), ["name", "message", "stack"]);
+});
+
+test("writes an instance of a class without toJSON as its class name, so the headers a request object keeps stay out", () => {
+	class ClientRequest {
+		_header = `POST /v1/oauth2/token HTTP/1.1\r\nAuthorization: Basic ${CREDENTIALS}\r\n\r\n`;
+		method = "POST";
+	}
+	const line = formatLogLine({ timestamp: TIMESTAMP, level: "error", message: "m", request: new ClientRequest(), seen: new Set([1]) });
+
+	assert.deepEqual(fieldsOf(line), { request: "[ClientRequest]", seen: "[Set]" });
+	assert.ok(!line.includes(CREDENTIALS), line);
+});
+
+test("writes an instance of a class with toJSON as what toJSON returns, redacted", () => {
+	// Like axios's AxiosHeaders, which an axios error carries in config.headers.
+	class AxiosHeaders {
+		toJSON() {
+			return { Accept: "application/json", Authorization: `Basic ${CREDENTIALS}` };
+		}
+	}
+	const at = new Date("2026-10-08T19:13:05.000Z");
+	const line = formatLogLine({ timestamp: TIMESTAMP, level: "error", message: "m", config: { headers: new AxiosHeaders() }, at });
+
+	assert.deepEqual(fieldsOf(line), {
+		config: { headers: { Accept: "application/json", Authorization: "[redacted]" } },
+		at: "2026-10-08T19:13:05.000Z"
+	});
+});
+
+test("writes a bigint as its digits and a field that cannot be read as [unreadable]", () => {
+	const unreadable = {
+		get value() {
+			throw new Error("no");
+		}
+	};
+	// The PayPal SDK keeps an OAuth token's expiry as a bigint, which JSON.stringify throws on.
+	const line = formatLogLine({ timestamp: TIMESTAMP, level: "debug", message: "m", expiry: 1791587585n, unreadable });
+
+	assert.deepEqual(fieldsOf(line), { expiry: "1791587585", unreadable: "[unreadable]" });
+});

tests/unit/order-state.test.ts

@@ -0,0 +1,56 @@
+import { test } from "node:test";
+import assert from "node:assert/strict";
+import { isLockedForCustomer, missingCheckoutFields } from "../../src/checkout/order-state.ts";
+
+// Shaped like the row PUT /orders/:uuid/cart reads with strapi.db.query("api::order.order").findOne before it updates.
+const order = (overrides = {}) => ({
+	id: 4711,
+	uuid: "11111111-2222-4333-8444-555555555555",
+	email: "erika@example.org",
+	paymentAuthorised: false,
+	paymentStatus: null,
+	invoiceSent: false,
+	...overrides
+});
+
+test("an order is open for the customer until its payment is authorised", () => {
+	assert.equal(isLockedForCustomer(order()), false);
+	// false is the schema's default, but a row can hold null
+	assert.equal(isLockedForCustomer(order({ paymentAuthorised: null })), false);
+	assert.equal(isLockedForCustomer({}), false);
+});
+
+test("an order is locked once its payment is authorised", () => {
+	// what capturePayment writes once the capture is verified (src/checkout/capture-payment.ts)
+	assert.equal(isLockedForCustomer(order({ paymentAuthorised: true, paymentStatus: "captured" })), true);
+	// what it wrote before
+	assert.equal(isLockedForCustomer(order({ paymentAuthorised: true, paymentStatus: "authorised" })), true);
+});
+
+// Shaped like the row POST /orders/:uuid/checkout reads (strapi.db.query findOne with orderDefaultParams), after both checkout steps.
+const readyForCheckout = (overrides = {}) =>
+	order({
+		invoiceAddress: "Erika Mustermann\nMusterstraße 1\n70190 Stuttgart",
+		deliveryAddress: "Erika Mustermann\nMusterstraße 1\n70190 Stuttgart",
+		delivery: { id: 1, name: "DHL", price: 4.95 },
+		...overrides
+	});
+
+test("an order that went through both checkout steps lacks nothing for the checkout", () => {
+	assert.deepEqual(missingCheckoutFields(readyForCheckout()), []);
+});
+
+test("names the email, invoice address and delivery method an order still lacks for the checkout", () => {
+	// a new order: POST /orders creates it empty
+	assert.deepEqual(missingCheckoutFields({ email: null, invoiceAddress: null, delivery: null }), ["email", "invoiceAddress", "delivery"]);
+	assert.deepEqual(missingCheckoutFields({}), ["email", "invoiceAddress", "delivery"]);
+	// after step 1 alone
+	assert.deepEqual(missingCheckoutFields(readyForCheckout({ invoiceAddress: null, deliveryAddress: null, delivery: null })), [
+		"invoiceAddress",
+		"delivery"
+	]);
+	assert.deepEqual(missingCheckoutFields(readyForCheckout({ email: "  " })), ["email"]);
+	assert.deepEqual(missingCheckoutFields(readyForCheckout({ invoiceAddress: "" })), ["invoiceAddress"]);
+	// a delivery method that was deleted is populated as null
+	assert.deepEqual(missingCheckoutFields(readyForCheckout({ delivery: null })), ["delivery"]);
+});

tests/unit/paypal-client.test.ts

@@ -0,0 +1,171 @@
+import { test } from "node:test";
+import assert from "node:assert/strict";
+import { PAYPAL_TIMEOUT_MS, breaksClient, createPayPalClient, paypalClientConfiguration } from "../../src/checkout/paypal-client.ts";
+
+const TOKEN_URL = "https://api-m.paypal.com/v1/oauth2/token";
+const ORDERS_URL = "https://api-m.paypal.com/v2/checkout/orders";
+const PAYPAL_ORDER = '{"id":"5O190127TN364715T","status":"CREATED"}';
+
+// What axios throws when PayPal cannot be reached: no status code, the request in config.
+const networkError = (url = TOKEN_URL) =>
+	Object.assign(new Error("getaddrinfo EAI_AGAIN api-m.paypal.com"), { name: "AxiosError", code: "EAI_AGAIN", config: { method: "post", url } });
+
+// What the SDK throws when PayPal answers with an error status (@apimatic/core's ApiError): the status code and the request.
+const apiError = (statusCode: number, url = ORDERS_URL) =>
+	Object.assign(new Error(`PayPal answered ${statusCode}`), { statusCode, request: { method: "POST", url }, headers: {}, body: "{}" });
+
+/**
+ * A fake of the SDK's OrdersController over a Client. Like the SDK, every client requests its OAuth token on its first call and
+ * keeps the promise for its lifetime, also when the token request failed: every later call fails with that same error and
+ * requests nothing. The token request fails while dns.up is false. Each construction and token request is counted.
+ */
+const fakeSdk = () => {
+	const sdk = { dnsUp: false, constructions: 0, tokenRequests: 0, configurations: [] as unknown[] };
+	const createController = (configuration: unknown) => {
+		sdk.constructions += 1;
+		sdk.configurations.push(configuration);
+		let token: Promise<string> | undefined;
+		const authenticate = () => {
+			if (token === undefined) {
+				sdk.tokenRequests += 1;
+				token = sdk.dnsUp ? Promise.resolve("A21AAF…") : Promise.reject(networkError());
+				token.catch(() => {});
+			}
+			return token;
+		};
+		return {
+			ordersCreate: async () => {
+				await authenticate();
+				return { statusCode: 201, body: PAYPAL_ORDER };
+			}
+		};
+	};
+	return { sdk, createController };
+};
+
+test("a client of the SDK keeps a failed token request: every later call fails without a request", async () => {
+	// What the replacement below works around, as the harness's scenario S7 observed with the real SDK.
+	const { sdk, createController } = fakeSdk();
+	const orders = createController({});
+
+	const first = await orders.ordersCreate().catch((error) => error);
+	sdk.dnsUp = true;
+	const second = await orders.ordersCreate().catch((error) => error);
+
+	assert.equal(second, first);
+	assert.equal(sdk.tokenRequests, 1);
+});
+
+test("replaces the client after a failed token request, so that the next call requests a new token", async () => {
+	const { sdk, createController } = fakeSdk();
+	const replaced: unknown[] = [];
+	const client = createPayPalClient({ configuration: {}, createController, onReplace: (error) => replaced.push(error) });
+
+	await assert.rejects(
+		client.call((orders) => orders.ordersCreate()),
+		{ name: "AxiosError", message: "getaddrinfo EAI_AGAIN api-m.paypal.com" }
+	);
+	assert.deepEqual([sdk.constructions, sdk.tokenRequests, replaced.length], [1, 1, 1]);
+
+	sdk.dnsUp = true;
+	assert.deepEqual(await client.call((orders) => orders.ordersCreate()), { statusCode: 201, body: PAYPAL_ORDER });
+	assert.deepEqual([sdk.constructions, sdk.tokenRequests], [2, 2]);
+
+	// The new client keeps its token.
+	await client.call((orders) => orders.ordersCreate());
+	assert.deepEqual([sdk.constructions, sdk.tokenRequests, replaced.length], [2, 2, 1]);
+});
+
+test("keeps the client after an answer of PayPal that leaves it usable", async () => {
+	let constructions = 0;
+	const client = createPayPalClient({
+		configuration: {},
+		createController: () => {
+			constructions += 1;
+			return { ordersCreate: async () => Promise.reject(apiError(422)) };
+		}
+	});
+
+	for (let call = 0; call < 3; call++) {
+		const error = await client.call((orders) => orders.ordersCreate()).catch((rejection) => rejection);
+		assert.equal(error.statusCode, 422);
+	}
+	assert.equal(constructions, 1);
+});
+
+test("a call that fails on a replaced client does not replace its successor", async () => {
+	let constructions = 0;
+	const pending: ((error: unknown) => void)[] = [];
+	const replaced: unknown[] = [];
+	const client = createPayPalClient({
+		configuration: {},
+		createController: () => {
+			constructions += 1;
+			return { ordersGet: () => new Promise<never>((_, reject) => pending.push(reject)) };
+		},
+		onReplace: (error) => replaced.push(error)
+	});
+
+	// Two calls run on the first client. The first one fails, which replaces the client, and a third call starts on the second.
+	const first = client.call((orders) => orders.ordersGet());
+	const second = client.call((orders) => orders.ordersGet());
+	pending[0](networkError(ORDERS_URL));
+	await assert.rejects(first);
+	const third = client.call((orders) => orders.ordersGet());
+	assert.equal(constructions, 2);
+
+	// The second call fails on the first client only now: the second client stays.
+	pending[1](networkError(ORDERS_URL));
+	await assert.rejects(second);
+	const fourth = client.call((orders) => orders.ordersGet());
+	assert.deepEqual([constructions, replaced.length], [2, 1]);
+
+	pending[2](apiError(404));
+	pending[3](apiError(404));
+	await Promise.all([assert.rejects(third), assert.rejects(fourth)]);
+});
+
+test("breaks the client with an error of the token request, without an answer, with 401 and with 5xx", () => {
+	for (const error of [
+		networkError(TOKEN_URL),
+		networkError(ORDERS_URL),
+		Object.assign(new Error("timeout of 15000ms exceeded"), { name: "AxiosError", code: "ECONNABORTED", config: { url: ORDERS_URL } }),
+		apiError(400, TOKEN_URL),
+		apiError(429, TOKEN_URL),
+		apiError(401, TOKEN_URL),
+		apiError(401, ORDERS_URL),
+		apiError(500, ORDERS_URL),
+		apiError(503, ORDERS_URL),
+		// The SDK's ResponseValidationError carries the status of the answer it could not read.
+		Object.assign(new Error("The response did not match the response schema."), { statusCode: 200, request: { url: TOKEN_URL } }),
+		new Error("The HTTP call was aborted."),
+		"a string",
+		undefined
+	]) {
+		assert.equal(breaksClient(error), true, String(error?.message ?? error));
+	}
+	for (const error of [apiError(400), apiError(404), apiError(409), apiError(422), apiError(429)]) {
+		assert.equal(breaksClient(error), false, error.message);
+	}
+});
+
+test("configures the SDK client with a timeout of 15 s and without logging bodies or headers", async () => {
+	const configuration = paypalClientConfiguration({ clientId: "DUMMY_CLIENT_ID", clientSecret: "DUMMY_CLIENT_SECRET", environment: "Production" });
+
+	assert.equal(PAYPAL_TIMEOUT_MS, 15000);
+	assert.deepEqual(configuration, {
+		clientCredentialsAuthCredentials: { oAuthClientId: "DUMMY_CLIENT_ID", oAuthClientSecret: "DUMMY_CLIENT_SECRET" },
+		timeout: 15000,
+		environment: "Production",
+		logging: { logRequest: { logBody: false, logHeaders: false }, logResponse: { logBody: false, logHeaders: false } }
+	});
+
+	// Every client the factory creates, also after a replacement, gets this configuration.
+	const { sdk, createController } = fakeSdk();
+	const client = createPayPalClient({ configuration, createController });
+	await client.call((orders) => orders.ordersCreate()).catch(() => {});
+	sdk.dnsUp = true;
+	await client.call((orders) => orders.ordersCreate());
+	assert.equal(sdk.constructions, 2);
+	for (const passed of sdk.configurations) assert.equal((passed as { timeout: number }).timeout, 15000);
+});

tests/unit/paypal-order.test.ts

@@ -1,6 +1,12 @@
 import { test } from "node:test";
 import assert from "node:assert/strict";
-import { buildPayPalOrderItems, buildPayPalOrderRequest } from "../../src/checkout/paypal-order.ts";
+import {
+	CheckoutNotReadyError,
+	ProductUnavailableError,
+	PRODUCT_UNAVAILABLE,
+	buildPayPalOrderRequest,
+	checkoutFailure
+} from "../../src/checkout/paypal-order.ts";
 import { calculateTotalProductPrice } from "../../src/checkout/pricing.ts";
 import { vatDecimal, vatIncludedDecimal } from "../../src/checkout/vat.ts";
 
@@ -27,7 +33,7 @@ const validOrder = (overrides = {}) => ({
 });
 
 // A cart of [price, count] lines with the totals the order service computes in update() (src/api/order/services/order.ts:151-173).
-const orderFor = (lines: [number, number][], deliveryPrice: number | null) => {
+const orderFor = (lines: [number, number][], deliveryPrice: number | null, paymentPrice: number | null = null) => {
 	const cart = lines.map(([price, count], index) => ({
 		id: index + 1,
 		count,
@@ -37,17 +43,15 @@ const orderFor = (lines: [number, number][], deliveryPrice: number | null) => {
 	return validOrder({
 		cart,
 		subtotal,
-		total: Math.round((subtotal + (deliveryPrice ?? 0)) * 100) / 100,
+		total: Math.round((subtotal + (deliveryPrice ?? 0) + (paymentPrice ?? 0)) * 100) / 100,
 		VAT: Math.round((subtotal / vatIncludedDecimal) * vatDecimal * 100) / 100,
-		delivery: deliveryPrice === null ? null : { id: 1, name: "DHL", price: deliveryPrice }
+		delivery: deliveryPrice === null ? null : { id: 1, name: "DHL", price: deliveryPrice },
+		payment: paymentPrice === null ? null : { id: 1, name: "Vorkasse", price: paymentPrice }
 	});
 };
 
-// Both halves in the order createSessionOrThrow runs them: what it would send to PayPal, or what it would throw.
-const buildSession = (order) => {
-	buildPayPalOrderItems(order);
-	return buildPayPalOrderRequest(RETURN_URL, order);
-};
+// What createSessionOrThrow would send to PayPal, or what it would throw before asking PayPal.
+const buildSession = (order) => buildPayPalOrderRequest(RETURN_URL, order);
 
 const cents = (money) => (money ? Math.round(Number(money.value) * 100) : 0);
 
@@ -71,6 +75,15 @@ const assertNoTypeError = (build: () => unknown) => {
 	}
 };
 
+const thrown = (build: () => unknown): unknown => {
+	try {
+		build();
+	} catch (error) {
+		return error;
+	}
+	assert.fail("did not throw");
+};
+
 // Characterization: what the builders do today.
 
 test("builds the PayPal order request for a valid order", () => {
@@ -117,85 +130,61 @@ test("sends no shipping amount when the order has no delivery method", () => {
 	});
 });
 
-test("rejects an order without a total before computing the items", () => {
-	for (const total of [0, null, undefined]) {
-		assert.throws(() => buildPayPalOrderItems(validOrder({ total })), { name: "Error", message: "Cart is empty or has no total" });
+// The request used to be built after a list of items that was never sent; computing it threw "Cart is empty or has no total".
+// That check now throws CheckoutNotReadyError, which the checkout answers 400 instead of 502.
+test("rejects an empty cart or an order without a total as not ready for checkout", () => {
+	for (const overrides of [{ total: 0 }, { total: null }, { total: undefined }, { cart: [] }, { cart: null }]) {
+		assert.throws(() => buildSession(validOrder(overrides)), { name: "CheckoutNotReadyError", message: "Cart is empty or has no total" });
 	}
 });
 
-test("computes one item per cart line, which is not sent to PayPal", () => {
-	const order = validOrder({
-		cart: [
-			{ id: 1, count: 1, product: notebook },
-			{ id: 2, count: 3, product: { id: 102, name: "Journaling Booklet", cover: { price: 12.5 } } }
-		]
-	});
+test("sends no items: amounts rounded per unit would miss the net and the VAT of the subtotal", () => {
+	// 3 × 12.50: per unit 10.50 net and 2.00 tax, 31.50 and 6.00 for the three; the subtotal of 37.50 has 31.51 net and 5.99 VAT.
+	const unitNetCents = Math.round((1250 * 100) / 119);
+	const unit = buildSession(orderFor([[12.5, 3]], 4.95)).purchaseUnits[0];
 
-	assert.deepEqual(buildPayPalOrderItems(order), [
-		{
-			name: "Notizbuch A5 Punktraster",
-			unitAmount: { currencyCode: "EUR", value: "15.04" },
-			tax: { currencyCode: "EUR", value: "2.86" },
-			quantity: "1"
-		},
-		{
-			name: "Journaling Booklet",
-			unitAmount: { currencyCode: "EUR", value: "10.50" },
-			tax: { currencyCode: "EUR", value: "2.00" },
-			quantity: "3"
+	assert.equal("items" in unit, false);
+	assert.deepEqual([3 * unitNetCents, 3 * (1250 - unitNetCents)], [3150, 600]);
+	assert.deepEqual(unit.amount, {
+		currencyCode: "EUR",
+		value: "42.45",
+		breakdown: {
+			itemTotal: { currencyCode: "EUR", value: "31.51" },
+			taxTotal: { currencyCode: "EUR", value: "5.99" },
+			shipping: { currencyCode: "EUR", value: "4.95" }
 		}
-	]);
+	});
 });
 
-// Known defects: these assert the correct behaviour and fail today, which the todo marks as expected.
+// Fixed defects of https://git.librete.ch/libretech/mp/issues/67.
 
-test(
-	"D1: a missing delivery address is rejected with a clear validation error",
-	{ todo: "null deliveryAddress throws a TypeError — https://git.librete.ch/libretech/mp/issues/67" },
-	() => {
+test("D1: a missing delivery address is rejected with a clear validation error", () => {
 	assert.throws(() => buildSession(validOrder({ deliveryAddress: null })), isClearError(/address/i));
-	}
-);
+});
 
-test(
-	"D2: a two-line delivery address does not throw a TypeError",
-	{ todo: "a two-line address throws a TypeError — https://git.librete.ch/libretech/mp/issues/67" },
-	() => {
+test("D2: a two-line delivery address does not throw a TypeError", () => {
 	assertNoTypeError(() => buildSession(validOrder({ deliveryAddress: "Erika Mustermann\nMusterstraße 1" })));
-	}
-);
+});
 
-test(
-	"D3: a pickup whose delivery price is null is sent with shipping 0.00",
-	{ todo: "delivery price null throws a TypeError — https://git.librete.ch/libretech/mp/issues/67" },
-	() => {
+test("D3: a pickup whose delivery price is null is sent with shipping 0.00", () => {
 	const order = validOrder({ delivery: { id: 2, name: "Abholung", price: null }, total: 17.9 });
 
 	assert.deepEqual(buildSession(order).purchaseUnits[0].amount.breakdown.shipping, { currencyCode: "EUR", value: "0.00" });
-	}
-);
+});
 
-test(
-	"D4: a cart line whose product was deleted is rejected with a clear error",
-	{ todo: "a deleted product throws a TypeError — https://git.librete.ch/libretech/mp/issues/67" },
-	() => {
+test("D4: a cart line whose product was deleted is rejected with a clear error", () => {
 	assert.throws(() => buildSession(validOrder({ cart: [{ id: 1, count: 1, product: null }] })), isClearError(/product/i));
-	}
-);
+});
 
-test(
-	"D5: with a payment surcharge the breakdown still adds up to the amount",
-	{ todo: "the surcharge is in the amount but not in the breakdown — https://git.librete.ch/libretech/mp/issues/67" },
-	() => {
+test("D5: with a payment surcharge the breakdown still adds up to the amount", () => {
 	// total = 17.90 + 4.95 shipping + 1.50 surcharge
 	const { amount } = buildSession(validOrder({ payment: { id: 1, name: "PayPal", price: 1.5 }, total: 24.35 })).purchaseUnits[0];
 
 	assert.equal(amount.value, "24.35");
 	assert.equal(breakdownCents(amount.breakdown), cents(amount));
-	}
-);
+});
 
-// Not a todo: this holds today for every whole-cent subtotal (Strapi stores prices as decimal(10,2)). It guards the fixes above.
+// This held before the fixes too, for every whole-cent subtotal (Strapi stores prices as decimal(10,2)). It guards the fixes above.
 test("D6: the breakdown adds up to the amount to the cent, also for the subtotals whose net is closest to half a cent", () => {
 	const carts: { lines: [number, number][]; delivery: number | null }[] = [
 		{ lines: [[17.9, 1]], delivery: 4.95 },
@@ -232,3 +221,187 @@ test("D6: the breakdown adds up to the amount to the cent, also for the subtotal
 	// Compare the count, not the array: diffing tens of thousands of entries against [] takes many GB of memory.
 	assert.equal(mismatches.length, 0, `${mismatches.length} carts do not add up, e.g. ${JSON.stringify(mismatches.slice(0, 3))}`);
 });
+
+// Shipping address: the structured delivery address, else the structured invoice address, else the text delivery address.
+
+const structured = (overrides = {}) => ({
+	givenName: "Erika",
+	familyName: "Mustermann",
+	streetAddress: "Musterstraße 1",
+	postalCode: "70190",
+	addressLevel2: "Stuttgart",
+	country: "DE",
+	...overrides
+});
+const berlin = structured({ givenName: "Max", streetAddress: "Hauptstraße 5", postalCode: "10115", addressLevel2: "Berlin" });
+const berlinShipping = {
+	name: { fullName: "Max Mustermann" },
+	address: { addressLine1: "Hauptstraße 5", postalCode: "10115", adminArea2: "Berlin", countryCode: "DE" }
+};
+// An address.structured-address component that was saved without components: Strapi fills in the default country.
+const emptyStructured = { givenName: null, familyName: null, streetAddress: null, postalCode: null, addressLevel2: null, country: "DE" };
+const shippingOf = (order) => buildSession(order).purchaseUnits[0].shipping;
+
+test("takes the shipping address from the structured delivery address before the invoice and the text address", () => {
+	assert.deepEqual(shippingOf(validOrder({ deliveryAddressStructured: berlin, invoiceAddressStructured: structured() })), berlinShipping);
+});
+
+test("falls back to the structured invoice address when no structured delivery address is entered", () => {
+	for (const deliveryAddressStructured of [null, undefined, emptyStructured, { givenName: "  ", country: "DE" }]) {
+		assert.deepEqual(
+			shippingOf(validOrder({ deliveryAddressStructured, invoiceAddressStructured: berlin, deliveryAddress: null })),
+			berlinShipping
+		);
+	}
+});
+
+test("trims the components, names the buyer by the name parts there are and upper-cases the country, DE by default", () => {
+	const order = (address) => validOrder({ deliveryAddressStructured: { ...structured(), ...address } });
+
+	assert.deepEqual(shippingOf(order({ givenName: " Erika ", familyName: null, streetAddress: " Musterstraße 1 ", country: "at" })), {
+		name: { fullName: "Erika" },
+		address: { addressLine1: "Musterstraße 1", postalCode: "70190", adminArea2: "Stuttgart", countryCode: "AT" }
+	});
+	for (const country of [null, undefined, ""]) {
+		assert.equal(shippingOf(order({ country })).address.countryCode, "DE");
+	}
+});
+
+test("rejects a structured address that is entered but incomplete instead of shipping to another address", () => {
+	const order = validOrder({ deliveryAddressStructured: structured({ streetAddress: "", postalCode: null }), invoiceAddressStructured: berlin });
+
+	assert.throws(() => buildSession(order), { name: "CheckoutNotReadyError", message: "deliveryAddressStructured lacks streetAddress, postalCode" });
+	assert.throws(() => buildSession(validOrder({ invoiceAddressStructured: structured({ givenName: null, familyName: "" }) })), {
+		name: "CheckoutNotReadyError",
+		message: "invoiceAddressStructured lacks givenName and familyName"
+	});
+	assert.throws(() => buildSession(validOrder({ deliveryAddressStructured: structured({ country: "Deutschland" }) })), {
+		name: "CheckoutNotReadyError",
+		message: "deliveryAddressStructured has no two-letter country code"
+	});
+});
+
+test("parses the text delivery address when no structured address is entered", () => {
+	const shippingFor = (deliveryAddress) => shippingOf(validOrder({ deliveryAddress, deliveryAddressStructured: emptyStructured }));
+
+	assert.deepEqual(shippingFor(" Erika Mustermann\r\nMusterstraße 1\r\n\r\n70190  Stuttgart-Bad Cannstatt \n"), {
+		name: { fullName: "Erika Mustermann" },
+		address: { addressLine1: "Musterstraße 1", postalCode: "70190", adminArea2: "Stuttgart-Bad Cannstatt", countryCode: "DE" }
+	});
+	// The street is the line above the postal code and city, as in a German address; the lines after the name go into addressLine2.
+	assert.deepEqual(shippingFor("Erika Mustermann\nc/o Muster GmbH\nHinterhaus\nMusterstraße 1\n70190 Stuttgart"), {
+		name: { fullName: "Erika Mustermann" },
+		address: {
+			addressLine1: "Musterstraße 1",
+			addressLine2: "c/o Muster GmbH, Hinterhaus",
+			postalCode: "70190",
+			adminArea2: "Stuttgart",
+			countryCode: "DE"
+		}
+	});
+});
+
+test("rejects a text delivery address it cannot parse, and a missing one, with a validation error", () => {
+	const cases: [unknown, string][] = [
+		["Erika Mustermann\nMusterstraße 1", "deliveryAddress needs the name, the street, and the postal code and city on lines of their own"],
+		["Erika Mustermann\n\nMusterstraße 1\n", "deliveryAddress needs the name, the street, and the postal code and city on lines of their own"],
+		["Erika Mustermann\nMusterstraße 1\n70190", "The last line of deliveryAddress is not the postal code and the city"],
+		["  \n ", "The order has no delivery address"],
+		["", "The order has no delivery address"],
+		[null, "The order has no delivery address"],
+		[undefined, "The order has no delivery address"]
+	];
+	for (const [deliveryAddress, message] of cases) {
+		assert.throws(() => buildSession(validOrder({ deliveryAddress })), { name: "CheckoutNotReadyError", message });
+	}
+});
+
+// Money in whole cents, and the errors the checkout answers.
+
+test("reads decimals that arrive as strings like numbers", () => {
+	const order = validOrder({ subtotal: "17.90", total: "22.85", VAT: "2.86", delivery: { id: 1, name: "DHL", price: "4.95" } });
+
+	assert.deepEqual(buildSession(order), buildSession(validOrder()));
+});
+
+test("rejects totals that do not add up, as after a price change, instead of sending PayPal a breakdown it rejects", () => {
+	// The delivery method costs 5.95 now; the order's total was computed when it cost 4.95.
+	assert.throws(() => buildSession(validOrder({ delivery: { id: 1, name: "DHL", price: 5.95 } })), {
+		name: "CheckoutNotReadyError",
+		message: "The order's totals do not add up: total 2285 cents, items 1504 + VAT 286 + shipping 595 + surcharge 0"
+	});
+	assert.throws(() => buildSession(validOrder({ delivery: { id: 1, name: "DHL", price: -4.95 }, total: 12.95 })), {
+		name: "CheckoutNotReadyError",
+		message: "The order's totals do not add up: total 1295 cents, items 1504 + VAT 286 + shipping -495 + surcharge 0"
+	});
+	for (const overrides of [{ VAT: null }, { subtotal: undefined }, { VAT: "n/a" }]) {
+		assert.throws(() => buildSession(validOrder(overrides)), { name: "CheckoutNotReadyError", message: "The order has no subtotal or no VAT" });
+	}
+});
+
+test("sends a payment surcharge as handling, and no handling for a payment method that costs nothing", () => {
+	const breakdownOf = (order) => buildSession(order).purchaseUnits[0].amount.breakdown;
+
+	assert.deepEqual(breakdownOf(validOrder({ payment: { id: 1, name: "PayPal", price: 1.5 }, total: 24.35 })), {
+		itemTotal: { currencyCode: "EUR", value: "15.04" },
+		taxTotal: { currencyCode: "EUR", value: "2.86" },
+		shipping: { currencyCode: "EUR", value: "4.95" },
+		handling: { currencyCode: "EUR", value: "1.50" }
+	});
+	for (const payment of [null, undefined, { id: 1, name: "PayPal", price: 0 }, { id: 1, name: "PayPal", price: null }]) {
+		assert.equal("handling" in breakdownOf(validOrder({ payment })), false);
+	}
+	// A surcharge the total lacks, as when the price of the payment method changed after the totals were computed.
+	assert.throws(() => buildSession(validOrder({ payment: { id: 1, name: "PayPal", price: 1.5 } })), {
+		name: "CheckoutNotReadyError",
+		message: "The order's totals do not add up: total 2285 cents, items 1504 + VAT 286 + shipping 495 + surcharge 150"
+	});
+});
+
+test("adds up to the cent with a surcharge, with a pickup without a price, for every whole-cent subtotal up to 300.00", () => {
+	const mismatches: string[] = [];
+	for (let cent = 1; cent <= 30000; cent++) {
+		for (const [delivery, payment] of [
+			[4.95, 0.35],
+			[0, 1.5]
+		]) {
+			const order = orderFor([[cent / 100, 1]], delivery, payment);
+			if (delivery === 0) order.delivery = { id: 2, name: "Abholung", price: null };
+			const { amount } = buildSession(order).purchaseUnits[0];
+			if (breakdownCents(amount.breakdown) !== cents(amount) || cents(amount.breakdown.handling) !== Math.round(payment * 100)) {
+				mismatches.push(`${cent}/${delivery}/${payment}`);
+			}
+		}
+	}
+
+	assert.equal(mismatches.length, 0, `${mismatches.length} carts do not add up, e.g. ${mismatches.slice(0, 3).join(", ")}`);
+});
+
+test("rejects a deleted product next to available ones as unavailable", () => {
+	const order = validOrder({ cart: [{ id: 1, count: 1, product: notebook }, { id: 2, count: 1, product: null }, null] });
+
+	assert.throws(
+		() => buildSession(order),
+		(error) => error instanceof ProductUnavailableError && error.name === "ProductUnavailableError" && error.message === PRODUCT_UNAVAILABLE
+	);
+});
+
+test("answers an order that is not ready 400 with the reason, a deleted product 409 and any other error 502", () => {
+	assert.deepEqual(checkoutFailure(thrown(() => buildSession(validOrder({ deliveryAddress: null })))), {
+		status: 400,
+		message: "Order is not ready for checkout",
+		reason: "The order has no delivery address"
+	});
+	assert.equal(checkoutFailure(thrown(() => buildSession(validOrder({ deliveryAddress: "Erika Mustermann\nMusterstraße 1" })))).status, 400);
+	assert.equal(checkoutFailure(thrown(() => buildSession(validOrder({ total: 0 })))).status, 400);
+	assert.deepEqual(checkoutFailure(thrown(() => buildSession(validOrder({ cart: [{ id: 1, count: 1, product: null }] })))), {
+		status: 409,
+		message: "A product in the cart is no longer available"
+	});
+	assert.ok(thrown(() => buildSession(validOrder({ total: 0 }))) instanceof CheckoutNotReadyError);
+
+	const sdkError = Object.assign(new Error("OAuth 2 provider says client authentication failed."), { statusCode: 401 });
+	for (const error of [sdkError, new TypeError("Cannot read properties of null (reading 'split')"), "/result/error", undefined]) {
+		assert.deepEqual(checkoutFailure(error), { status: 502, message: "Could not create the PayPal order" });
+	}
+});

tests/unit/paypal-verify.test.ts

@@ -0,0 +1,260 @@
+import { test } from "node:test";
+import assert from "node:assert/strict";
+import { readFileSync } from "node:fs";
+import { orderTotalCents, parseCents, verifyApprovedOrder, verifyCompletedCapture } from "../../src/checkout/paypal-verify.ts";
+import { buildPayPalOrderRequest } from "../../src/checkout/paypal-order.ts";
+
+const UUID = "11111111-2222-4333-8444-555555555555";
+
+// PayPal's Orders v2 JSON as PayPalApi parses the response body: the PayPal order once the buyer approved it
+// (GET /v2/checkout/orders/:id), and the PayPal order after its capture (POST /v2/checkout/orders/:id/capture with
+// Prefer: return=representation). Both belong to the order below. Every call returns a fresh copy to change.
+const fixture = (name: string) => JSON.parse(readFileSync(new URL(`./fixtures/${name}`, import.meta.url), "utf8"));
+const approved = () => fixture("paypal-order-approved.json");
+const captured = () => fixture("paypal-order-captured.json");
+
+// The order of paypal-order.test.ts: subtotal 17.90, delivery 4.95, total 22.85.
+const order = (overrides = {}) => ({
+	id: 4711,
+	uuid: UUID,
+	email: "erika@example.org",
+	subtotal: 17.9,
+	total: 22.85,
+	VAT: 2.86,
+	delivery: { id: 1, name: "DHL", price: 4.95 },
+	invoiceNumber: "R-12-4711",
+	cart: [
+		{ id: 1, count: 1, product: { id: 101, name: "Notizbuch A5 Punktraster", cover: { price: 14.9 }, pages: { price: 3 }, ruling: { price: 0 } } }
+	],
+	deliveryAddress: "Erika Mustermann\nMusterstraße 1\n70190 Stuttgart",
+	...overrides
+});
+
+// What identifies the buyer or the merchant in the fixtures. A reason is logged, so it repeats none of it.
+const PERSONAL_DATA = [
+	"Erika",
+	"Mustermann",
+	"erika",
+	"QYR5Z8XDVJNXQ",
+	"Musterstraße",
+	"70190",
+	"Stuttgart",
+	"merchant@example.com",
+	"7KNGBPH2U58GQ"
+];
+
+/** The reason of a rejection, after checking that it repeats no personal data. */
+const rejection = (result: { ok: boolean; reason?: string }): string => {
+	assert.equal(result.ok, false, "expected a rejection");
+	for (const value of PERSONAL_DATA) assert.ok(!result.reason.includes(value), `the reason repeats ${value}: ${result.reason}`);
+	return result.reason;
+};
+
+// Money
+
+test("parses PayPal's money values into integer cents", () => {
+	assert.equal(parseCents("22.85"), 2285);
+	assert.equal(parseCents("0.01"), 1);
+	assert.equal(parseCents("4.9"), 490);
+	assert.equal(parseCents("100"), 10000);
+	assert.equal(parseCents("0.00"), 0);
+	assert.equal(parseCents("1234567.89"), 123456789);
+});
+
+test("parses nothing but a non-negative amount with at most two decimals", () => {
+	for (const value of ["", "22.850", "-22.85", "22,85", " 22.85", "22.85 ", "2.285e1", "22.", ".85", "0x10", "Infinity", "NaN", "12345678901.00"]) {
+		assert.equal(parseCents(value), null, JSON.stringify(value));
+	}
+	for (const value of [22.85, null, undefined, {}, ["22.85"]]) {
+		assert.equal(parseCents(value), null, String(value));
+	}
+});
+
+test("turns the order total into integer cents, also where its float is a hair below the cent", () => {
+	// 22.85 * 100 is 2284.9999999999995 and 0.29 * 100 is 28.999999999999996 in floating point
+	assert.equal(orderTotalCents({ total: 22.85 }), 2285);
+	assert.equal(orderTotalCents({ total: 0.29 }), 29);
+	assert.equal(orderTotalCents({ total: 17.9 + 4.95 }), 2285);
+	for (const total of [null, undefined, 0, -4.95, NaN, Infinity]) {
+		assert.equal(orderTotalCents({ total }), null, String(total));
+	}
+});
+
+test("the amount the checkout sends PayPal is the amount the capture accepts, for every total up to 3000.00", () => {
+	const mismatches: number[] = [];
+	for (let cents = 1; cents <= 300000; cents++) {
+		// The order service rounds every total to the cent; an order without a delivery method has its subtotal as its total.
+		const total = cents / 100;
+		const VAT = Math.round((total / 1.19) * 0.19 * 100) / 100;
+		const request = buildPayPalOrderRequest("https://shop.example/checkout/3", order({ subtotal: total, total, VAT, delivery: null }));
+		const { amount } = request.purchaseUnits[0];
+		if (parseCents(amount.value) !== cents || orderTotalCents({ total }) !== cents) mismatches.push(total);
+	}
+	assert.equal(mismatches.length, 0, `e.g. ${mismatches.slice(0, 5).join(", ")}`);
+});
+
+test("the fixtures belong to the PayPal order the checkout requests for the order", () => {
+	const request = buildPayPalOrderRequest("https://shop.example/checkout/3", order()).purchaseUnits[0];
+
+	for (const paypalOrder of [approved(), captured()]) {
+		const unit = paypalOrder.purchase_units[0];
+		assert.equal(unit.custom_id, request.customId);
+		assert.equal(unit.amount.value, request.amount.value);
+		assert.equal(unit.amount.currency_code, request.amount.currencyCode);
+	}
+});
+
+// The PayPal order the buyer approved
+
+test("accepts the PayPal order the buyer approved for the order", () => {
+	assert.deepEqual(verifyApprovedOrder(order(), approved()), { ok: true });
+});
+
+test("rejects a PayPal order that is not approved", () => {
+	for (const status of ["CREATED", "SAVED", "PAYER_ACTION_REQUIRED", "VOIDED", "COMPLETED"]) {
+		assert.equal(rejection(verifyApprovedOrder(order(), { ...approved(), status })), `the PayPal order status is ${status}, not APPROVED`);
+	}
+	const { status, ...withoutStatus } = approved();
+	assert.equal(rejection(verifyApprovedOrder(order(), withoutStatus)), "the PayPal order status is missing or unexpected, not APPROVED");
+	// a value that is not one of PayPal's statuses is not repeated
+	assert.equal(
+		rejection(verifyApprovedOrder(order(), { ...approved(), status: "APPROVED BY ERIKA MUSTERMANN" })),
+		"the PayPal order status is missing or unexpected, not APPROVED"
+	);
+});
+
+test("rejects the PayPal order of a cheap order captured for an expensive one", () => {
+	// The buyer pays order A, then calls the capture of order B with A's PayPal order.
+	const orderB = order({ id: 4712, uuid: "99999999-8888-4777-8666-555555555555", total: 249 });
+
+	assert.equal(rejection(verifyApprovedOrder(orderB, approved())), "the custom_id of the PayPal order is not the order's uuid");
+});
+
+test("rejects a PayPal order without a custom_id, also for an order without a uuid", () => {
+	const paypalOrder = approved();
+	delete paypalOrder.purchase_units[0].custom_id;
+
+	assert.equal(rejection(verifyApprovedOrder(order(), paypalOrder)), "the custom_id of the PayPal order is not the order's uuid");
+	// undefined is not compared with undefined, nor "" with ""
+	assert.equal(
+		rejection(verifyApprovedOrder(order({ uuid: undefined }), paypalOrder)),
+		"the custom_id of the PayPal order is not the order's uuid"
+	);
+	paypalOrder.purchase_units[0].custom_id = "";
+	assert.equal(rejection(verifyApprovedOrder(order({ uuid: "" }), paypalOrder)), "the custom_id of the PayPal order is not the order's uuid");
+});
+
+test("rejects a PayPal order whose amount is not the order total", () => {
+	const withAmount = (value: unknown) => {
+		const paypalOrder = approved();
+		paypalOrder.purchase_units[0].amount.value = value;
+		return paypalOrder;
+	};
+
+	assert.equal(rejection(verifyApprovedOrder(order(), withAmount("22.84"))), "the PayPal order amount 22.84 is not the order total 22.85");
+	assert.equal(rejection(verifyApprovedOrder(order(), withAmount("22.86"))), "the PayPal order amount 22.86 is not the order total 22.85");
+	assert.equal(rejection(verifyApprovedOrder(order(), withAmount("2285"))), "the PayPal order amount 2285.00 is not the order total 22.85");
+	// the cart changed after the checkout
+	assert.equal(rejection(verifyApprovedOrder(order({ total: 249 }), approved())), "the PayPal order amount 22.85 is not the order total 249.00");
+	for (const value of ["22.850", "22,85", "", 22.85, null]) {
+		assert.equal(rejection(verifyApprovedOrder(order(), withAmount(value))), "the PayPal order amount is not a money value", String(value));
+	}
+});
+
+test("rejects a PayPal order in another currency or without an amount", () => {
+	const paypalOrder = approved();
+	paypalOrder.purchase_units[0].amount.currency_code = "USD";
+	assert.equal(rejection(verifyApprovedOrder(order(), paypalOrder)), "the PayPal order currency is USD, not EUR");
+
+	paypalOrder.purchase_units[0].amount.currency_code = "Euro";
+	assert.equal(rejection(verifyApprovedOrder(order(), paypalOrder)), "the PayPal order currency is missing or unexpected, not EUR");
+
+	delete paypalOrder.purchase_units[0].amount;
+	assert.equal(rejection(verifyApprovedOrder(order(), paypalOrder)), "the PayPal order has no amount");
+});
+
+test("rejects every PayPal order for an order without a total", () => {
+	for (const total of [null, 0]) {
+		assert.equal(rejection(verifyApprovedOrder(order({ total }), approved())), "the order has no total");
+	}
+});
+
+test("rejects a PayPal order without a purchase unit, and anything that is not a PayPal order", () => {
+	assert.equal(rejection(verifyApprovedOrder(order(), { ...approved(), purchase_units: [] })), "the PayPal order has no purchase unit");
+	const { purchase_units, ...withoutUnits } = approved();
+	assert.equal(rejection(verifyApprovedOrder(order(), withoutUnits)), "the PayPal order has no purchase unit");
+
+	// "/result/error" is what PayPalApi.checkPaymentStatus answered for every error
+	for (const value of [null, undefined, "/result/error", [], 42]) {
+		assert.equal(rejection(verifyApprovedOrder(order(), value)), "the PayPal order is not an object", String(value));
+	}
+});
+
+// The PayPal order after the capture
+
+test("accepts the completed capture of the order total and returns the capture id", () => {
+	assert.deepEqual(verifyCompletedCapture(order(), captured()), { ok: true, captureId: "3C679366HH908993F" });
+});
+
+test("rejects a capture response whose PayPal order is not completed", () => {
+	for (const status of ["APPROVED", "PAYER_ACTION_REQUIRED", "VOIDED"]) {
+		assert.equal(rejection(verifyCompletedCapture(order(), { ...captured(), status })), `the PayPal order status is ${status}, not COMPLETED`);
+	}
+});
+
+test("rejects a capture PayPal holds for review, declined or refunded", () => {
+	for (const status of ["PENDING", "DECLINED", "FAILED", "REFUNDED", "PARTIALLY_REFUNDED"]) {
+		const response = captured();
+		response.purchase_units[0].payments.captures[0].status = status;
+		if (status === "PENDING") response.purchase_units[0].payments.captures[0].status_details = { reason: "PENDING_REVIEW" };
+
+		assert.equal(rejection(verifyCompletedCapture(order(), response)), `the capture status is ${status}, not COMPLETED`);
+	}
+});
+
+test("rejects a capture response without a capture", () => {
+	// what PayPal answers with Prefer: return=minimal, which the capture used to ask for
+	const minimal = { id: "5O190127TN364715T", status: "COMPLETED", links: captured().links };
+	assert.equal(rejection(verifyCompletedCapture(order(), minimal)), "the capture response has no capture");
+
+	const withoutPayments = captured();
+	delete withoutPayments.purchase_units[0].payments;
+	assert.equal(rejection(verifyCompletedCapture(order(), withoutPayments)), "the capture response has no capture");
+
+	const withoutCaptures = captured();
+	withoutCaptures.purchase_units[0].payments.captures = [];
+	assert.equal(rejection(verifyCompletedCapture(order(), withoutCaptures)), "the capture response has no capture");
+
+	assert.equal(rejection(verifyCompletedCapture(order(), { ...captured(), purchase_units: [] })), "the capture response has no capture");
+});
+
+test("rejects a capture of another amount or in another currency", () => {
+	const lower = captured();
+	lower.purchase_units[0].payments.captures[0].amount.value = "2.29";
+	assert.equal(rejection(verifyCompletedCapture(order(), lower)), "the capture amount 2.29 is not the order total 22.85");
+
+	// the cart changed during the capture
+	assert.equal(rejection(verifyCompletedCapture(order({ total: 249 }), captured())), "the capture amount 22.85 is not the order total 249.00");
+
+	const usd = captured();
+	usd.purchase_units[0].payments.captures[0].amount.currency_code = "USD";
+	assert.equal(rejection(verifyCompletedCapture(order(), usd)), "the capture currency is USD, not EUR");
+
+	const withoutAmount = captured();
+	delete withoutAmount.purchase_units[0].payments.captures[0].amount;
+	assert.equal(rejection(verifyCompletedCapture(order(), withoutAmount)), "the capture has no amount");
+});
+
+test("rejects a capture without a valid id", () => {
+	for (const id of [undefined, "", 12345, "3C679366HH908993F; Erika Mustermann", "x".repeat(65)]) {
+		const response = captured();
+		response.purchase_units[0].payments.captures[0].id = id;
+		assert.equal(rejection(verifyCompletedCapture(order(), response)), "the capture has no valid id", String(id));
+	}
+});
+
+test("rejects anything that is not a capture response", () => {
+	for (const value of [null, undefined, "/result/error", [], 42]) {
+		assert.equal(rejection(verifyCompletedCapture(order(), value)), "the capture response is not an object", String(value));
+	}
+});

types/generated/contentTypes.d.ts

@@ -389,7 +389,10 @@ export interface ApiOrderOrder extends Schema.CollectionType {
 		invoiceSent: Attribute.Boolean & Attribute.DefaultTo<false>;
 		payment: Attribute.Relation<"api::order.order", "oneToOne", "api::payment.payment">;
 		paymentAuthorised: Attribute.Boolean & Attribute.DefaultTo<false>;
+		paymentCapturedAt: Attribute.DateTime & Attribute.Private;
 		paymentStatus: Attribute.String;
+		paypalCaptureId: Attribute.String & Attribute.Private;
+		paypalOrderId: Attribute.String & Attribute.Private;
 		subtotal: Attribute.Decimal;
 		total: Attribute.Decimal;
 		updatedAt: Attribute.DateTime;