feat: configure explicit CORS with allowed origins whitelist

backend/src/config.js

@@ -16,6 +16,8 @@ const schema = z.object({
   SEP10_SERVER_KEY: z.string().min(1),
   JWT_SECRET: z.string().min(1),
   PORT: z.coerce.number().int().positive().default(4000),
+  // Comma-separated list of allowed origins, e.g. https://app.example.com,https://admin.example.com
+  ALLOWED_ORIGINS: z.string().default('http://localhost:3000'),
 
   // Transaction fees (stroops; 1 XLM = 10_000_000 stroops)
   SOROBAN_FEE: z.coerce.number().int().positive().default(100),

backend/tests/cors.test.js

@@ -0,0 +1,47 @@
+const request = require('supertest');
+
+describe('CORS', () => {
+  const ALLOWED = 'http://localhost:3000';
+  const BLOCKED = 'https://evil.example.com';
+
+  let app;
+
+  beforeEach(() => {
+    jest.resetModules();
+    process.env.ALLOWED_ORIGINS = ALLOWED;
+    app = require('../src/app');
+  });
+
+  it('allows requests from an allowed origin', async () => {
+    const res = await request(app).get('/health').set('Origin', ALLOWED);
+    expect(res.headers['access-control-allow-origin']).toBe(ALLOWED);
+  });
+
+  it('blocks requests from a disallowed origin', async () => {
+    const res = await request(app).get('/health').set('Origin', BLOCKED);
+    expect(res.headers['access-control-allow-origin']).toBeUndefined();
+  });
+
+  it('handles preflight for allowed origin', async () => {
+    const res = await request(app)
+      .options('/health')
+      .set('Origin', ALLOWED)
+      .set('Access-Control-Request-Method', 'GET');
+    expect(res.status).toBe(204);
+    expect(res.headers['access-control-allow-origin']).toBe(ALLOWED);
+  });
+
+  it('sets credentials header for allowed origin', async () => {
+    const res = await request(app).get('/health').set('Origin', ALLOWED);
+    expect(res.headers['access-control-allow-credentials']).toBe('true');
+  });
+
+  it('supports multiple allowed origins', async () => {
+    jest.resetModules();
+    process.env.ALLOWED_ORIGINS = `${ALLOWED},https://admin.example.com`;
+    const multiApp = require('../src/app');
+
+    const res = await request(multiApp).get('/health').set('Origin', 'https://admin.example.com');
+    expect(res.headers['access-control-allow-origin']).toBe('https://admin.example.com');
+  });
+});