Authenticate Using Google Sign-In on Apple Platforms

You can let your users authenticate with Firebase using their Google Accounts by integrating Google Sign-In into your app.

Before you begin

Add Firebase to your Apple project. Include the following pods in your Podfile:
```
pod 'FirebaseAuth'
pod 'GoogleSignIn'
```
If you haven't yet connected your app to your Firebase project, do so from the Firebase console.
Enable Google as a sign-in method in the Firebase console:
1. In the Firebase console, open the Auth section.
2. On the Sign in method tab, enable the Google sign-in method and click Save.

1. Import the required header files

First, you must import the Firebase SDK and Google Sign-In SDK header files into your app.

Swift

import FirebaseCore
import GoogleSignIn

Objective-C

@import FirebaseCore;
@import GoogleSignIn;

2. Implement Google Sign-In

Implement Google Sign-In by following these steps. See the Google Sign-In developer documentation for details on using Google Sign-In with iOS.

Add custom URL schemes to your Xcode project:

Open your project configuration: double-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.
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 blank.
When completed, your config should look something similar to the following (but with your application-specific values):

In your app delegate's application:didFinishLaunchingWithOptions: method, configure the FirebaseApp object.

Swift

// Use Firebase library to configure APIs
FirebaseApp.configure()

Objective-C

// Use Firebase library to configure APIs
[FIRApp configure];

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

@available(iOS 9.0, *)
func application(_ application: UIApplication, open url: URL,
                 options: [UIApplication.OpenURLOptionsKey: Any])
  -> Bool {
  return GIDSignIn.sharedInstance.handle(url)
}

Objective-C

- (BOOL)application:(nonnull UIApplication *)application
            openURL:(nonnull NSURL *)url
            options:(nonnull NSDictionary<NSString *, id> *)options {
  return [[GIDSignIn sharedInstance] handleURL:url];
}

Pass the presenting view controller and client ID for your app to the Google Sign In sign-in method and create a Firebase auth credential from the resulting Google auth token:

Swift

guard let clientID = FirebaseApp.app()?.options.clientID else { return }

// Create Google Sign In configuration object.
let config = GIDConfiguration(clientID: clientID)

// Start the sign in flow!
GIDSignIn.sharedInstance.signIn(with: config, presenting: self) { [unowned self] user, error in

  if let error = error {
    // ...
    return
  }

  guard
    let authentication = user?.authentication,
    let idToken = authentication.idToken
  else {
    return
  }

  let credential = GoogleAuthProvider.credential(withIDToken: idToken,
                                                 accessToken: authentication.accessToken)

  // ...
}

Objective-C

GIDConfiguration *config = [[GIDConfiguration alloc] initWithClientID:[FIRApp defaultApp].options.clientID];

__weak __auto_type weakSelf = self;
[GIDSignIn.sharedInstance signInWithConfiguration:config presentingViewController:self callback:^(GIDGoogleUser * _Nullable user, NSError * _Nullable error) {
  __auto_type strongSelf = weakSelf;
  if (strongSelf == nil) { return; }

  if (error == nil) {
    GIDAuthentication *authentication = user.authentication;
    FIRAuthCredential *credential =
    [FIRGoogleAuthProvider credentialWithIDToken:authentication.idToken
                                     accessToken:authentication.accessToken];
    // ...
  } else {
    // ...
  }
}];

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.
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.
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.
```
@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 object.
Objective-C
1. In your view controller's header file, declare the sign-in button as a property.
```
@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 object.

3. Authenticate with Firebase

Finally, complete the Firebase login process with the auth credential created in the previous step.

Swift

Auth.auth().signIn(with: credential) { authResult, error in
    if let error = error {
      let authError = error as NSError
      if isMFAEnabled, authError.code == AuthErrorCode.secondFactorRequired.rawValue {
        // The user is a multi-factor user. Second factor challenge is required.
        let resolver = authError
          .userInfo[AuthErrorUserInfoMultiFactorResolverKey] as! MultiFactorResolver
        var displayNameString = ""
        for tmpFactorInfo in resolver.hints {
          displayNameString += tmpFactorInfo.displayName ?? ""
          displayNameString += " "
        }
        self.showTextInputPrompt(
          withMessage: "Select factor to sign in\n\(displayNameString)",
          completionBlock: { userPressedOK, displayName in
            var selectedHint: PhoneMultiFactorInfo?
            for tmpFactorInfo in resolver.hints {
              if displayName == tmpFactorInfo.displayName {
                selectedHint = tmpFactorInfo as? PhoneMultiFactorInfo
              }
            }
            PhoneAuthProvider.provider()
              .verifyPhoneNumber(with: selectedHint!, uiDelegate: nil,
                                 multiFactorSession: resolver
                                   .session) { verificationID, error in
                if error != nil {
                  print(
                    "Multi factor start sign in failed. Error: \(error.debugDescription)"
                  )
                } else {
                  self.showTextInputPrompt(
                    withMessage: "Verification code for \(selectedHint?.displayName ?? "")",
                    completionBlock: { userPressedOK, verificationCode in
                      let credential: PhoneAuthCredential? = PhoneAuthProvider.provider()
                        .credential(withVerificationID: verificationID!,
                                    verificationCode: verificationCode!)
                      let assertion: MultiFactorAssertion? = PhoneMultiFactorGenerator
                        .assertion(with: credential!)
                      resolver.resolveSignIn(with: assertion!) { authResult, error in
                        if error != nil {
                          print(
                            "Multi factor finanlize sign in failed. Error: \(error.debugDescription)"
                          )
                        } else {
                          self.navigationController?.popViewController(animated: true)
                        }
                      }
                    }
                  )
                }
              }
          }
        )
      } else {
        self.showMessagePrompt(error.localizedDescription)
        return
      }
      // ...
      return
    }
    // User is signed in
    // ...
}

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 FIRUser object. See Manage Users.
In your Firebase Realtime Database and Cloud Storage Security Rules, 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.

To sign out a user, call signOut:.

Swift

    let firebaseAuth = Auth.auth()
do {
  try firebaseAuth.signOut()
} catch let signOutError as NSError {
  print("Error signing out: %@", signOutError)
}

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.