fix(auth0): skip profile cache when id_token has no sub claim

When the JWT id_token lacks a sub claim, the cache key would be
auth0-profile:undefined, causing all users without a sub to share
the same cached profile. Now skips caching entirely when sub is
missing and fetches the profile directly.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Signed-off-by: Jack Palmer <jackpalmer@spotify.com>

plugins/auth-backend-module-auth0-provider/src/authenticator.test.ts

@@ -242,4 +242,47 @@ describe('createAuth0Authenticator', () => {
     expect(mockFetchProfile).toHaveBeenCalledTimes(2);
     expect(result.fullProfile).toEqual(updatedProfile);
   });
+
+  it('should skip cache when id_token has no sub claim', async () => {
+    const header = Buffer.from(JSON.stringify({ alg: 'none' })).toString(
+      'base64url',
+    );
+    const payload = Buffer.from(JSON.stringify({ aud: 'test' })).toString(
+      'base64url',
+    );
+    const idTokenWithoutSub = `${header}.${payload}.`;
+
+    mockExecuteRefresh.mockResolvedValue({
+      accessToken: 'new-access-token',
+      refreshToken: 'new-refresh-token',
+      params: {
+        token_type: 'bearer',
+        scope: 'openid profile',
+        expires_in: 3600,
+        id_token: idTokenWithoutSub,
+      },
+    });
+
+    const authenticator = createAuth0Authenticator({ cache });
+    const ctx = authenticator.initialize({
+      callbackUrl: 'http://localhost/callback',
+      config: mockConfig,
+    });
+
+    const result = await authenticator.refresh(
+      {
+        refreshToken: 'my-refresh-token',
+        scope: 'openid profile',
+        req: {} as express.Request,
+      },
+      ctx,
+    );
+
+    // Profile is fetched directly
+    expect(mockFetchProfile).toHaveBeenCalledWith('new-access-token');
+    expect(result.fullProfile).toEqual(mockProfile);
+    // Cache is never read or written
+    expect(cache.get).not.toHaveBeenCalled();
+    expect(cache.set).not.toHaveBeenCalled();
+  });
 });

plugins/auth-backend-module-auth0-provider/src/authenticator.ts

@@ -140,17 +140,20 @@ export function createAuth0Authenticator(options?: { cache?: CacheService }) {
       );
 
       const { sub } = decodeJwt(result.params.id_token);
-      const cacheKey = `auth0-profile:${sub}`;
-      let fullProfile = (await profileCache?.get(cacheKey)) as
-        | PassportProfile
-        | undefined;
+      const cacheKey = sub ? `auth0-profile:${sub}` : undefined;
+
+      let fullProfile = cacheKey
+        ? ((await profileCache?.get(cacheKey)) as PassportProfile | undefined)
+        : undefined;
 
       if (!fullProfile) {
         fullProfile = await helper.fetchProfile(result.accessToken);
-        await profileCache?.set(
-          cacheKey,
-          JSON.parse(JSON.stringify(fullProfile)),
-        );
+        if (cacheKey) {
+          await profileCache?.set(
+            cacheKey,
+            JSON.parse(JSON.stringify(fullProfile)),
+          );
+        }
       }
 
       return {