fix: Implement IP-based rate limiting with Redis for DDoS protection

stellar-payment-platform/server.js

@@ -926,8 +926,24 @@ app.get('/users', validateSchema({ query: usersQuerySchema }), async (req, res,
 // Mount v1 router for both legacy paths and explicit API versioning
 app.use('/', v1Router);
 app.use('/api/v1', v1Router);
+// #492 — Strict rate limiter for auth/login endpoints. These are prime
+// brute-force targets, so they get a much tighter budget than the global
+// limiter. Uses the same Redis-backed store so the limit is shared across
+// all distributed nodes.
+const authLimiter = rateLimit({
+  windowMs: 15 * 60 * 1000,
+  max: 20,
+  store: redisClient ? new RedisStore({
+    sendCommand: (...args) => redisClient.sendCommand(args),
+  }) : undefined,
+  standardHeaders: true,
+  legacyHeaders: true,
+  message: errorBody('RATE_LIMITED', 'Too many requests, please try again later.'),
+  keyGenerator: (req) => req.ip || (req.connection && req.connection.remoteAddress) || '',
+});
+
 // Auth endpoints (email OTP verification) - uses Redis when available
-app.use('/auth', require('./src/routes/v1/authRoutes')(redisClient));
+app.use('/auth', authLimiter, require('./src/routes/v1/authRoutes')(redisClient));
 
 // #497 — Expose RSA public key as a JWKS document so external services can
 // verify RS256-signed tokens without sharing a secret.

stellar-payment-platform/tests/rate-limit.test.js

@@ -250,6 +250,33 @@ describe('Rate Limiting — express-rate-limit', () => {
     });
   });
 
+  // ── Strict auth/login rate limit ─────────────────────────────────────────
+
+  describe('strict auth rate limit', () => {
+    it('applies a stricter limit on /auth endpoints than the global limiter', async () => {
+      // The auth limiter allows only 20 requests per window, so the 21st
+      // request should be rejected even though the global limit is 100.
+      for (let i = 0; i < 20; i++) {
+        await request(app)
+          .post('/auth/verify-email')
+          .send({ email: `user${i}@example.com` });
+      }
+
+      const res = await request(app)
+        .post('/auth/verify-email')
+        .send({ email: 'overflow@example.com' });
+
+      expect(res.status).toBe(429);
+      expect(res.body).toEqual({
+        success: false,
+        error: {
+          code: 'RATE_LIMITED',
+          message: 'Too many requests, please try again later.',
+        },
+      });
+    });
+  });
+
   // ── Reset between test modules ───────────────────────────────────────────
 
   describe('rate limiter resets with new app instance', () => {