You can let your users authenticate with Firebase using their Google Accounts by integrating Google Sign-In into your app. ### AI prompt for AI assistance ***For AI assistance, copy the prompt below into your AI coding agent (like Antigravity, Claude Code, Codex, and Cursor).** You can customize the prompt and iterate with your agent. Visit [Firebase agent skills](https://firebase.google.com/docs/ai-assistance/agent-skills.md.txt) for detailed installation info.* ``` Help me use Firebase in my app. 1. Make sure that **Firebase agent skills** are installed and updated. For Claude Code, Codex, or Cursor agents, help me install the Firebase plugin. For other agents, run `npx skills add firebase/agent-skills`. Always try to use **Firebase agent skills** for Firebase-related tasks. 2. Help me set up and use Firebase Authentication with Google Sign-In in my app. ``` ## Before you begin [Video](https://www.youtube.com/watch?v=IzyOdKm0bWE) Use Swift Package Manager to install and manage Firebase dependencies. > [!NOTE] > Visit [our installation guide](https://firebase.google.com/docs/ios/installation-methods.md.txt) to learn about the different ways you can add Firebase SDKs to your Apple project. 1. In Xcode, with your app project open, navigate to **File \> Add Packages**. 2. When prompted, add the Firebase Apple platforms SDK repository: ``` https://github.com/firebase/firebase-ios-sdk.git ``` > [!NOTE] > **Note:** New projects should use the default (latest) SDK version, but you can choose an older version if needed. 3. Choose the Firebase Authentication library. 4. Add the `-ObjC` flag to the *Other Linker Flags* section of your target's build settings. 5. When finished, Xcode will automatically begin resolving and downloading your dependencies in the background. ## Add the Google Sign-In SDK to your project 1. In Xcode, with your app project open, navigate to **File \> Add Packages**. 2. When prompted, add the Google Sign-In SDK repository: https://github.com/google/GoogleSignIn-iOS 3. When finished, Xcode will automatically begin resolving and downloading your dependencies in the background. ## Enable Google Sign-In for your Firebase project To allow users to sign in using Google Sign-In, you must first enable the Google Sign-In provider for your Firebase project: 1. In the Firebase console, go to **Security** \> [**Authentication**](https://console.firebase.google.com/project/_/authentication/). 2. In the **Sign-in method** tab, enable the **Google** provider. 3. Click **Save**. 4. Download a new copy of your project's `GoogleService-Info.plist` file and copy it to your Xcode project. Overwrite any existing versions with the new one. (See [Add Firebase to your iOS project](https://firebase.google.com/docs/ios/setup.md.txt#add-config-file).) ## Import the required header files First, you must import the Firebase SDK and Google Sign-In SDK header files into your app. #### Swift ```swift import FirebaseAuth import GoogleSignIn ``` #### Objective-C ```objective-c @import FirebaseCore; @import GoogleSignIn; ``` ## Implement Google Sign-In Implement Google Sign-In by following these steps. See the [Google Sign-In developer documentation](https://developers.google.com/identity/sign-in/ios) for details on using Google Sign-In with iOS. 1. Add custom URL schemes to your Xcode project: 1. Open your project configuration: click the project name in the left tree view. Select your app from the **TARGETS** section, then select the **Info** tab, and expand the **URL Types** section. 2. Click the **+** button, and add a URL scheme for your reversed client ID. To find this value, open the `` `GoogleService-Info.plist` `` configuration file, and look for the `REVERSED_CLIENT_ID` key. Copy the value of that key, and paste it into the **URL Schemes** box on the configuration page. Leave the other fields untouched. When completed, your config should look something similar to the following (but with your application-specific values): ![](https://firebase.google.com/static/docs/auth/images/xcode_infotab_url_type_values.png) 2. In your app delegate's `application:didFinishLaunchingWithOptions:` method, configure the `FirebaseApp` object. #### Swift ```swift // Use Firebase library to configure APIs FirebaseApp.configure() ``` #### Objective-C ```objective-c // Use Firebase library to configure APIs [FIRApp configure]; ``` 3. Implement the `application:openURL:options:` method of your app delegate. The method should call the `handleURL` method of the `GIDSignIn` instance, which will properly handle the URL that your application receives at the end of the authentication process. #### Swift ```swift func scene(_ scene: UIScene, openURLContexts URLContexts: Set) { // ... } return GIDSignIn.sharedInstance.handle(url) } ``` #### Objective-C ```objective-c - (BOOL)application:(nonnull UIApplication *)application openURL:(nonnull NSURL *)url options:(nonnull NSDictionary *)options { return [[GIDSignIn sharedInstance] handleURL:url]; } ``` 4. Pass the presenting view controller and client ID for your app to the `signIn` method of the Google Sign-In provider and create a Firebase Authentication credential from the resulting Google auth token: #### Swift ```swift guard let clientID = FirebaseApp.app()?.options.clientID else { return } // Create Google Sign In configuration object. let config = GIDConfiguration(clientID: clientID) GIDSignIn.sharedInstance.configuration = config // Start the sign in flow! GIDSignIn.sharedInstance.signIn(withPresenting: viewController) { result, error in guard error == nil else { // ... return } guard let user = result?.user, let idToken = user.idToken?.tokenString else { // ... return } let credential = GoogleAuthProvider.credential(withIDToken: idToken, accessToken: user.accessToken.tokenString) self.signIn(with: credential) } ``` #### Objective-C ```objective-c GIDConfiguration *config = [[GIDConfiguration alloc] initWithClientID:[FIRApp defaultApp].options.clientID]; [GIDSignIn.sharedInstance setConfiguration:config]; __weak __auto_type weakSelf = self; [GIDSignIn.sharedInstance signInWithPresentingViewController:self completion:^(GIDSignInResult * _Nullable result, NSError * _Nullable error) { __auto_type strongSelf = weakSelf; if (strongSelf == nil) { return; } if (error == nil) { FIRAuthCredential *credential = [FIRGoogleAuthProvider credentialWithIDToken:result.user.idToken.tokenString accessToken:result.user.accessToken.tokenString]; // ... } else { // ... } }]; ``` 5. Add a `GIDSignInButton` to your storyboard, XIB file, or instantiate it programmatically. To add the button to your storyboard or XIB file, add a View and set its custom class to `GIDSignInButton`. > [!NOTE] > When you add a `GIDSignInButton` view to your storyboard, the sign-in button doesn't render in the interface builder. Run the app to see the sign-in button. 6. **Optional** : If you want to customize the button, do the following: #### Swift 1. In your view controller, declare the sign-in button as a property. ```swift @IBOutlet weak var signInButton: GIDSignInButton! ``` 2. Connect the button to the `signInButton` property you just declared. 3. Customize the button by setting the properties of the [GIDSignInButton](https://developers.google.com/identity/sign-in/ios/api/interface_g_i_d_sign_in_button#property-summary) object. #### Objective-C 1. In your view controller's header file, declare the sign-in button as a property. ```objective-c @property(weak, nonatomic) IBOutlet GIDSignInButton *signInButton; ``` 2. Connect the button to the `signInButton` property you just declared. 3. Customize the button by setting the properties of the [GIDSignInButton](https://developers.google.com/identity/sign-in/ios/api/interface_g_i_d_sign_in_button#property-summary) object. ## Authenticate with Firebase Finally, complete the Firebase login process with the auth credential created in the previous step. #### Swift ```swift Auth.auth().signIn(with: credential) { result, error in guard error == nil else { // ... return } // At this point, our user is signed in } ``` #### Objective-C ```objective-c [[FIRAuth auth] signInWithCredential:credential completion:^(FIRAuthDataResult * _Nullable authResult, NSError * _Nullable error) { if (isMFAEnabled && error && error.code == FIRAuthErrorCodeSecondFactorRequired) { FIRMultiFactorResolver *resolver = error.userInfo[FIRAuthErrorUserInfoMultiFactorResolverKey]; NSMutableString *displayNameString = [NSMutableString string]; for (FIRMultiFactorInfo *tmpFactorInfo in resolver.hints) { [displayNameString appendString:tmpFactorInfo.displayName]; [displayNameString appendString:@" "]; } [self showTextInputPromptWithMessage:[NSString stringWithFormat:@"Select factor to sign in\n%@", displayNameString] completionBlock:^(BOOL userPressedOK, NSString *_Nullable displayName) { FIRPhoneMultiFactorInfo* selectedHint; for (FIRMultiFactorInfo *tmpFactorInfo in resolver.hints) { if ([displayName isEqualToString:tmpFactorInfo.displayName]) { selectedHint = (FIRPhoneMultiFactorInfo *)tmpFactorInfo; } } [FIRPhoneAuthProvider.provider verifyPhoneNumberWithMultiFactorInfo:selectedHint UIDelegate:nil multiFactorSession:resolver.session completion:^(NSString * _Nullable verificationID, NSError * _Nullable error) { if (error) { [self showMessagePrompt:error.localizedDescription]; } else { [self showTextInputPromptWithMessage:[NSString stringWithFormat:@"Verification code for %@", selectedHint.displayName] completionBlock:^(BOOL userPressedOK, NSString *_Nullable verificationCode) { FIRPhoneAuthCredential *credential = [[FIRPhoneAuthProvider provider] credentialWithVerificationID:verificationID verificationCode:verificationCode]; FIRMultiFactorAssertion *assertion = [FIRPhoneMultiFactorGenerator assertionWithCredential:credential]; [resolver resolveSignInWithAssertion:assertion completion:^(FIRAuthDataResult * _Nullable authResult, NSError * _Nullable error) { if (error) { [self showMessagePrompt:error.localizedDescription]; } else { NSLog(@"Multi factor finanlize sign in succeeded."); } }]; }]; } }]; }]; } else if (error) { // ... return; } // User successfully signed in. Get user data from the FIRUser object if (authResult == nil) { return; } FIRUser *user = authResult.user; // ... }]; ``` ## Next steps After a user signs in for the first time, a new user account is created and linked to the credentials---that is, the user name and password, phone number, or auth provider information---the user signed in with. This new account is stored as part of your Firebase project, and can be used to identify a user across every app in your project, regardless of how the user signs in. - In your apps, you can get the user's basic profile information from the [`User`](https://firebase.google.com/docs/reference/ios/firebaseauth/interface_f_i_r_user) object. See [Manage Users](https://firebase.google.com/docs/auth/ios/manage-users.md.txt). - In your Firebase Realtime Database and Cloud Storage [Security Rules](https://firebase.google.com/docs/database/security/user-security), you can get the signed-in user's unique user ID from the `auth` variable, and use it to control what data a user can access. You can allow users to sign in to your app using multiple authentication providers by [linking auth provider credentials to an existing user account.](https://firebase.google.com/docs/auth/ios/account-linking) To sign out a user, call [`signOut:`](https://firebase.google.com/docs/reference/ios/firebaseauth/interface_f_i_r_auth#ab0d5111f05c3f1906243852cc8ef41b1). #### Swift ```swift let firebaseAuth = Auth.auth() do { try firebaseAuth.signOut() } catch let signOutError as NSError { print("Error signing out: %@", signOutError) } ``` #### Objective-C ```objective-c NSError *signOutError; BOOL status = [[FIRAuth auth] signOut:&signOutError]; if (!status) { NSLog(@"Error signing out: %@", signOutError); return; } ``` You may also want to add error handling code for the full range of authentication errors. See [Handle Errors](https://firebase.google.com/docs/auth/ios/errors.md.txt).