fix(oidc): normalize id_token iss claim before issuer comparison (#837)

jwt.verify does an exact string match on the issuer. Providers like
Authentik include a trailing slash in the id_token iss claim while the
configured issuer is already normalized (no trailing slash), causing
every login attempt to fail with jwt issuer invalid.

Move the issuer check out of jwt.verify options and apply the same
trailing-slash normalization used in the discovery doc validation.
Also adds OIDC-SVC-033–036 unit tests covering exact match, trailing
slash, wrong issuer, and wrong audience cases.

Closes #834

server/src/services/oidcService.ts

@@ -313,7 +313,6 @@ export async function verifyIdToken(
   try {
     const verified = jwt.verify(idToken, publicKey, {
       algorithms: [alg as jwt.Algorithm],
-      issuer: expectedIssuer,
       audience: clientId,
     });
     claims = typeof verified === 'string' ? {} : (verified as Record<string, unknown>);
@@ -322,6 +321,13 @@ export async function verifyIdToken(
     return { ok: false, error: `signature_or_claim_mismatch: ${msg}` };
   }
 
+  // Normalize trailing slash before issuer comparison — some IdPs (e.g. Authentik)
+  // include a trailing slash in the id_token iss claim.
+  const tokenIssuer = typeof claims['iss'] === 'string' ? claims['iss'].replace(/\/+$/, '') : '';
+  if (tokenIssuer !== expectedIssuer) {
+    return { ok: false, error: `signature_or_claim_mismatch: jwt issuer invalid. expected: ${expectedIssuer}` };
+  }
+
   return { ok: true, claims };
 }
 

server/tests/unit/services/oidcService.test.ts

@@ -4,6 +4,8 @@
  * discover caching, and the ReDoS-sensitive issuer trailing-slash regex.
  */
 import { describe, it, expect, vi, beforeAll, beforeEach, afterAll, afterEach } from 'vitest';
+import { generateKeyPairSync } from 'crypto';
+import jwtLib from 'jsonwebtoken';
 
 // ── DB setup ──────────────────────────────────────────────────────────────────
 
@@ -50,6 +52,7 @@ import {
   frontendUrl,
   findOrCreateUser,
   discover,
+  verifyIdToken,
 } from '../../../src/services/oidcService';
 
 const MOCK_CONFIG = {
@@ -460,3 +463,66 @@ describe('getUserInfo', () => {
     expect(fetchCall[1].headers.Authorization).toBe('Bearer access-token-123');
   });
 });
+
+// ── verifyIdToken ─────────────────────────────────────────────────────────────
+
+describe('verifyIdToken', () => {
+  const { privateKey, publicKey } = generateKeyPairSync('rsa', { modulusLength: 2048 });
+  const jwk = publicKey.export({ format: 'jwk' }) as Record<string, unknown>;
+  const ISSUER = 'https://auth.example.com/application/o/trek';
+  const CLIENT_ID = 'trek-client';
+  const JWKS_URI = 'https://auth.example.com/.well-known/jwks.json';
+
+  function mockJwks() {
+    vi.stubGlobal('fetch', vi.fn().mockResolvedValue({
+      ok: true,
+      json: async () => ({ keys: [jwk] }),
+    }));
+  }
+
+  function makeToken(iss: string, overrides: object = {}) {
+    return jwtLib.sign(
+      { sub: 'user-sub', email: 'user@example.com', ...overrides },
+      privateKey,
+      { algorithm: 'RS256', audience: CLIENT_ID, issuer: iss, expiresIn: '1h' }
+    );
+  }
+
+  const doc = { jwks_uri: JWKS_URI } as any;
+
+  afterEach(() => { vi.unstubAllGlobals(); });
+
+  it('OIDC-SVC-033: accepts token whose iss matches expectedIssuer exactly', async () => {
+    mockJwks();
+    const token = makeToken(ISSUER);
+    const result = await verifyIdToken(token, doc, CLIENT_ID, ISSUER);
+    expect(result.ok).toBe(true);
+  });
+
+  it('OIDC-SVC-034: accepts token whose iss has a trailing slash (Authentik)', async () => {
+    mockJwks();
+    const token = makeToken(ISSUER + '/');
+    const result = await verifyIdToken(token, doc, CLIENT_ID, ISSUER);
+    expect(result.ok).toBe(true);
+  });
+
+  it('OIDC-SVC-035: rejects token with wrong issuer', async () => {
+    mockJwks();
+    const token = makeToken('https://evil.example.com');
+    const result = await verifyIdToken(token, doc, CLIENT_ID, ISSUER);
+    expect(result.ok).toBe(false);
+    expect((result as any).error).toMatch('jwt issuer invalid');
+  });
+
+  it('OIDC-SVC-036: rejects token with wrong audience', async () => {
+    mockJwks();
+    const token = makeToken(ISSUER, {});
+    const wrongAudToken = jwtLib.sign(
+      { sub: 'user-sub', iss: ISSUER },
+      privateKey,
+      { algorithm: 'RS256', audience: 'wrong-client', expiresIn: '1h' }
+    );
+    const result = await verifyIdToken(wrongAudToken, doc, CLIENT_ID, ISSUER);
+    expect(result.ok).toBe(false);
+  });
+});