Implement Firebase Auth UseUserAccessGroup for C++ SDK

auth/integration_test/src/integration_test.cc

@@ -1513,4 +1513,47 @@ TEST_F(FirebaseAuthTest, TestLinkFederatedProviderBadProviderIdFails) {
 
 #endif  // defined(ENABLE_OAUTH_TESTS)
 
+TEST_F(FirebaseAuthTest, TestUseUserAccessGroup) {
+  // This test simply calls the UseUserAccessGroup method to ensure it doesn't
+  // crash. It doesn't verify the underlying keychain behavior.
+  // On non-iOS platforms, this is a no-op and should return kAuthErrorNone.
+  // On iOS, it will call the underlying OS method.
+
+  LogDebug("Calling UseUserAccessGroup with a test group ID.");
+  firebase::auth::AuthError error =
+      auth_->UseUserAccessGroup("com.firebase.test.accessgroup");
+
+#if TARGET_OS_IPHONE
+  // On iOS, the actual error code depends on keychain access and provisioning.
+  // For this test, we just ensure it doesn't crash.
+  // A specific error like kAuthErrorMissingIOSBundleID might occur if the
+  // environment isn't set up for keychain sharing, or kAuthErrorNone on
+  // success. For a simple "does not crash" test, we don't strictly check
+  // the error code, but kAuthErrorNone is the ideal outcome if keychain is
+  // usable.
+  LogDebug("UseUserAccessGroup returned %d on iOS.", error);
+#else
+  // On other platforms, it should be a no-op.
+  EXPECT_EQ(error, firebase::auth::kAuthErrorNone);
+#endif
+
+  LogDebug("Calling UseUserAccessGroup with nullptr to clear the group.");
+  error = auth_->UseUserAccessGroup(nullptr);
+
+#if TARGET_OS_IPHONE
+  LogDebug("UseUserAccessGroup(nullptr) returned %d on iOS.", error);
+#else
+  EXPECT_EQ(error, firebase::auth::kAuthErrorNone);
+#endif
+
+  LogDebug("Calling UseUserAccessGroup with empty string to clear the group.");
+  error = auth_->UseUserAccessGroup("");
+
+#if TARGET_OS_IPHONE
+  LogDebug("UseUserAccessGroup(\"\") returned %d on iOS.", error);
+#else
+  EXPECT_EQ(error, firebase::auth::kAuthErrorNone);
+#endif
+}
+
 }  // namespace firebase_testapp_automated

auth/src/android/auth_android.cc

@@ -676,5 +676,14 @@ void DisableTokenAutoRefresh(AuthData* auth_data) {}
 void InitializeTokenRefresher(AuthData* auth_data) {}
 void DestroyTokenRefresher(AuthData* auth_data) {}
 
+// Stub implementation for UseUserAccessGroupInternal on Android.
+AuthError UseUserAccessGroupInternal(AuthData* auth_data,
+                                     const char* group_id) {
+  // This function is a no-op on Android.
+  (void)auth_data;
+  (void)group_id;
+  return kAuthErrorNone;
+}
+
 }  // namespace auth
 }  // namespace firebase

auth/src/auth.cc

@@ -373,5 +373,12 @@ AUTH_RESULT_FN(Auth, SignInWithEmailAndPassword, AuthResult)
 
 AUTH_RESULT_FN(Auth, CreateUserWithEmailAndPassword, AuthResult)
 
+AuthError Auth::UseUserAccessGroup(const char* group_id) {
+  if (!auth_data_) {
+    return kAuthErrorUninitialized;
+  }
+  return UseUserAccessGroupInternal(auth_data_, group_id);
+}
+
 }  // namespace auth
 }  // namespace firebase

auth/src/desktop/auth_desktop.cc

@@ -768,5 +768,14 @@ void IdTokenRefreshThread::DisableAuthRefresh() {
   ref_count_--;
 }
 
+// Stub implementation for UseUserAccessGroupInternal on desktop.
+AuthError UseUserAccessGroupInternal(AuthData* auth_data,
+                                     const char* group_id) {
+  // This function is a no-op on desktop platforms.
+  (void)auth_data;
+  (void)group_id;
+  return kAuthErrorNone;
+}
+
 }  // namespace auth
 }  // namespace firebase

auth/src/include/firebase/auth.h

@@ -517,6 +517,23 @@ class Auth {
   /// not available on the current device.
   static Auth* GetAuth(App* app, InitResult* init_result_out = nullptr);
 
+  /// @brief Sets the user access group to use for data sharing for the app.
+  ///
+  /// This method is only applicable to iOS. On other platforms, it's a no-op
+  /// and will return `kAuthErrorNone`.
+  ///
+  /// Sets the user access group to use for data sharing for the app. This
+  /// should be used to share authentication data between apps that have the
+  /// same access group.
+  ///
+  /// @param[in] group_id The user access group to use. For example,
+  /// `com.example.accessgroup`. Set to `nullptr` or an empty string to clear
+  /// a previously set value and use the default keychain group.
+  ///
+  /// @return Returns `kAuthErrorNone` on success, or an `AuthError` code if an
+  /// error occurred.
+  AuthError UseUserAccessGroup(const char* group_id);
+
  private:
   /// @cond FIREBASE_APP_INTERNAL
   friend class ::firebase::App;

auth/src/ios/auth_ios.mm

@@ -608,5 +608,17 @@ void DisableTokenAutoRefresh(AuthData *auth_data) {}
 void InitializeTokenRefresher(AuthData *auth_data) {}
 void DestroyTokenRefresher(AuthData *auth_data) {}
 
+AuthError UseUserAccessGroupInternal(AuthData* auth_data,
+                                     const char* group_id) {
+  NSString* group_id_nsstring = nil;
+  if (group_id != nullptr && strlen(group_id) > 0) {
+    group_id_nsstring = [NSString stringWithUTF8String:group_id];
+  }
+
+  NSError* ns_error = nil;
+  [AuthImpl(auth_data) useUserAccessGroup:group_id_nsstring error:&ns_error];
+  return AuthErrorFromNSError(ns_error);
+}
+
 }  // namespace auth
 }  // namespace firebase