refactor: simplify MPP pay credential creation

packages/cli/src/__tests__/cli.test.ts

@@ -803,6 +803,20 @@ describe('production mode', () => {
       'expires="2099-01-01T00:00:00Z"',
     ].join(' ');
 
+    const WWW_AUTHENTICATE_MULTI = [
+      'Payment id="tempo_001",',
+      'realm="127.0.0.1",',
+      'method="tempo",',
+      'intent="charge",',
+      'request="e30=",',
+      'Payment id="ch_001",',
+      'realm="127.0.0.1",',
+      'method="stripe",',
+      'intent="charge",',
+      `request="${Buffer.from(JSON.stringify({ networkId: 'net_001', amount: '1000', currency: 'usd', decimals: 2, paymentMethodTypes: ['card'] })).toString('base64')}",`,
+      'expires="2099-01-01T00:00:00Z"',
+    ].join(' ');
+
     it('happy path: probes, gets 402, signs, retries, returns response', async () => {
       setNextResponse(200, APPROVED_SPT_REQUEST);
       setMerchantResponse(402, '{"error":"payment required"}', {
@@ -830,6 +844,27 @@ describe('production mode', () => {
       expect(merchantRequests[1].headers.authorization).toMatch(/^Payment /);
     });
 
+    it('selects the stripe challenge when the response advertises multiple methods', async () => {
+      setNextResponse(200, APPROVED_SPT_REQUEST);
+      setMerchantResponse(402, '{"error":"payment required"}', {
+        'www-authenticate': WWW_AUTHENTICATE_MULTI,
+      });
+      setMerchantResponse(200, '{"success":true}');
+
+      const result = await runProdCli(
+        'mpp',
+        'pay',
+        `http://127.0.0.1:${merchantPort}/api/charge`,
+        '--spend-request-id',
+        'lsrq_spt_001',
+        '--output-json',
+      );
+
+      expect(result.exitCode).toBe(0);
+      expect(merchantRequests).toHaveLength(2);
+      expect(merchantRequests[1].headers.authorization).toMatch(/^Payment /);
+    });
+
     it('passthrough: no 402 returns response without signing', async () => {
       setNextResponse(200, APPROVED_SPT_REQUEST);
       setMerchantResponse(200, '{"ok":true}');

packages/cli/src/commands/mpp/decode.ts

@@ -1,5 +1,17 @@
 import { Challenge } from 'mppx';
 
+type StripeChargeChallenge = Challenge.Challenge<
+  Record<string, unknown>,
+  'charge',
+  'stripe'
+>;
+
+type ResolvedStripeChallenge = {
+  challenge: StripeChargeChallenge;
+  networkId: string;
+  request: Record<string, unknown>;
+};
+
 export interface DecodedStripeChallenge {
   id: string;
   realm: string;
@@ -46,11 +58,9 @@ function getMethodDetails(
   return methodDetails as Record<string, unknown>;
 }
 
-export function decodeStripeChallenge(
-  challengeHeader: string,
-): DecodedStripeChallenge {
-  const challenges = Challenge.deserializeList(challengeHeader);
-
+function resolveStripeChallenge(
+  challenges: Challenge.Challenge[],
+): ResolvedStripeChallenge {
   const stripeChallenge = challenges.find(
     (challenge) =>
       challenge.method === 'stripe' && challenge.intent === 'charge',
@@ -88,13 +98,33 @@ export function decodeStripeChallenge(
   }
 
   return {
-    id: stripeChallenge.id,
-    realm: stripeChallenge.realm,
+    challenge: stripeChallenge as StripeChargeChallenge,
+    networkId,
+    request,
+  };
+}
+
+export function getStripeChargeChallengeFromResponse(
+  response: Response,
+): StripeChargeChallenge {
+  return resolveStripeChallenge(Challenge.fromResponseList(response)).challenge;
+}
+
+export function decodeStripeChallenge(
+  challengeHeader: string,
+): DecodedStripeChallenge {
+  const { challenge, networkId, request } = resolveStripeChallenge(
+    Challenge.deserializeList(challengeHeader),
+  );
+
+  return {
+    id: challenge.id,
+    realm: challenge.realm,
     method: 'stripe',
     intent: 'charge',
-    description: stripeChallenge.description,
-    digest: stripeChallenge.digest,
-    expires: stripeChallenge.expires,
+    description: challenge.description,
+    digest: challenge.digest,
+    expires: challenge.expires,
     network_id: networkId,
     request_json: request,
   };

packages/cli/src/commands/mpp/pay.tsx

@@ -1,10 +1,12 @@
 import type { ISpendRequestResource } from '@stripe/link-sdk';
 import { Box, Text } from 'ink';
 import Spinner from 'ink-spinner';
-import { Challenge, Credential } from 'mppx';
+import { Credential, Method } from 'mppx';
+import { Mppx, Transport } from 'mppx/client';
+import { Methods as StripeMethods } from 'mppx/stripe';
 import React, { useEffect, useState } from 'react';
 import { outputError } from '../../utils/execute-command';
-import { decodeStripeChallenge } from './decode';
+import { getStripeChargeChallengeFromResponse } from './decode';
 
 export type PayResult = {
   status: number;
@@ -30,6 +32,36 @@ function buildHeaders(
   return result;
 }
 
+function createStripePaymentClient(spt: string) {
+  const stripeCharge = Method.toClient(StripeMethods.charge, {
+    async createCredential({ challenge }) {
+      return Credential.serialize({
+        challenge,
+        payload: { spt },
+      });
+    },
+  });
+
+  return Mppx.create({
+    methods: [stripeCharge],
+    polyfill: false,
+    transport: Transport.from<RequestInit, Response>({
+      name: 'stripe-http',
+      isPaymentRequired(response) {
+        return response.status === 402;
+      },
+      getChallenge(response) {
+        return getStripeChargeChallengeFromResponse(response);
+      },
+      setCredential(request, credential) {
+        const nextHeaders = new Headers(request.headers);
+        nextHeaders.set('Authorization', credential);
+        return { ...request, headers: nextHeaders };
+      },
+    }),
+  });
+}
+
 export async function runMppPay(
   url: string,
   spendRequestId: string,
@@ -91,27 +123,10 @@ export async function runMppPay(
     return { status: initialResponse.status, headers: responseHeaders, body };
   }
 
-  // 5. Parse challenges, find stripe
-  const decoded = decodeStripeChallenge(
-    initialResponse.headers.get('www-authenticate') ?? '',
-  );
-  const stripeChallenge = Challenge.from({
-    id: decoded.id,
-    realm: decoded.realm,
-    method: decoded.method,
-    intent: decoded.intent,
-    request: decoded.request_json,
-    ...(decoded.description ? { description: decoded.description } : {}),
-    ...(decoded.digest ? { digest: decoded.digest } : {}),
-    ...(decoded.expires ? { expires: decoded.expires } : {}),
-  });
-
-  // 6. Build and serialize credential
-  const credential = Credential.from({
-    challenge: stripeChallenge,
-    payload: { spt },
-  });
-  const authHeader = Credential.serialize(credential);
+  // 5. Select the Stripe challenge and build the payment credential
+  const authHeader = await createStripePaymentClient(
+    spt,
+  ).createCredential(initialResponse);
 
   // 7. Retry with Authorization header
   const retryResponse = await fetch(url, {
@@ -211,25 +226,9 @@ export function MppPay({
         }
 
         setStep('signing');
-        const decoded = decodeStripeChallenge(
-          initialResponse.headers.get('www-authenticate') ?? '',
-        );
-        const stripeChallenge = Challenge.from({
-          id: decoded.id,
-          realm: decoded.realm,
-          method: decoded.method,
-          intent: decoded.intent,
-          request: decoded.request_json,
-          ...(decoded.description ? { description: decoded.description } : {}),
-          ...(decoded.digest ? { digest: decoded.digest } : {}),
-          ...(decoded.expires ? { expires: decoded.expires } : {}),
-        });
-
-        const credential = Credential.from({
-          challenge: stripeChallenge,
-          payload: { spt },
-        });
-        const authHeader = Credential.serialize(credential);
+        const authHeader = await createStripePaymentClient(
+          spt,
+        ).createCredential(initialResponse);
 
         setStep('submitting');
         const retryResponse = await fetch(url, {