Authenticate Using Google Sign-In on iOS

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

Before you begin

1. Add Firebase to your iOS project. Include the following pods in your Podfile:

   pod 'Firebase/Auth'
   pod 'GoogleSignIn'
   

2. If you haven't yet connected your app to your Firebase project, do so from the Firebase console.
3. Enable Google Sign-In 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.

import Firebase
import GoogleSignIn

import Firebase
import GoogleSignIn

@import Firebase;
@import GoogleSignIn;

@import Firebase;
@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.

1. Add custom URL schemes to your Xcode project:
1. 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.
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 blank.

   When completed, your config should look something similar to the following (but with your application-specific values):

   
2. Declare that the app delegate implements the GIDSignInDelegate protocol.

   Swift

   In AppDelegate.swift:

   class AppDelegate: UIResponder, UIApplicationDelegate, GIDSignInDelegate {
   

   Objective-C

   In AppDelegate.h:

   @interface AppDelegate : UIResponder<UIApplicationDelegate, GIDSignInDelegate>
   

3. In your app delegate's application:didFinishLaunchingWithOptions: method, configure the FirebaseApp object and set the sign-in delegate.

   Swift

   // Use Firebase library to configure APIs
   FirebaseApp.configure()
   
   GIDSignIn.sharedInstance().clientID = FirebaseApp.app()?.options.clientID
   GIDSignIn.sharedInstance().delegate = self
   

   Objective-C

   // Use Firebase library to configure APIs
   [FIRApp configure];
   
   [GIDSignIn sharedInstance].clientID = [FIRApp defaultApp].options.clientID;
   [GIDSignIn sharedInstance].delegate = self;
   

4. 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];
   }
   

   For your app to run on iOS 8 and older, also implement the deprecated application:openURL:sourceApplication:annotation: method.

   Swift

   func application(_ application: UIApplication, open url: URL, sourceApplication: String?, annotation: Any) -> Bool {
       return GIDSignIn.sharedInstance().handle(url)
   }
   

   Objective-C

   - (BOOL)application:(UIApplication *)application
               openURL:(NSURL *)url
     sourceApplication:(NSString *)sourceApplication
            annotation:(id)annotation {
     return [[GIDSignIn sharedInstance] handleURL:url];
   }
   

5. In the app delegate, implement the GIDSignInDelegate protocol to handle the sign-in process by defining the following methods:

   Objective-C

   - (void)signIn:(GIDSignIn *)signIn
   didSignInForUser:(GIDGoogleUser *)user
        withError:(NSError *)error {
     // ...
     if (error == nil) {
       GIDAuthentication *authentication = user.authentication;
       FIRAuthCredential *credential =
       [FIRGoogleAuthProvider credentialWithIDToken:authentication.idToken
                                        accessToken:authentication.accessToken];
       // ...
     } else {
       // ...
     }
   }
   
   - (void)signIn:(GIDSignIn *)signIn
   didDisconnectWithUser:(GIDGoogleUser *)user
        withError:(NSError *)error {
     // Perform any operations when the user disconnects from app here.
     // ...
   }
   

   Swift

   func sign(_ signIn: GIDSignIn!, didSignInFor user: GIDGoogleUser!, withError error: Error?) {
     // ...
     if let error = error {
       // ...
       return
     }
   
     guard let authentication = user.authentication else { return }
     let credential = GoogleAuthProvider.credential(withIDToken: authentication.idToken,
                                                       accessToken: authentication.accessToken)
     // ...
   }
   
   func sign(_ signIn: GIDSignIn!, didDisconnectWith user: GIDGoogleUser!, withError error: Error!) {
       // Perform any operations when the user disconnects from app here.
       // ...
   }
   

6. In the view controller, override the viewDidLoad method to set the presenting view controller of the GIDSignIn object, and (optionally) to sign in silently when possible.

   Objective-C

   [GIDSignIn sharedInstance].presentingViewController = self;
   [[GIDSignIn sharedInstance] signIn];
   

   Swift

   GIDSignIn.sharedInstance()?.presentingViewController = self
   GIDSignIn.sharedInstance().signIn()
   

7. 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.
8. 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

In the signIn:didSignInForUser:withError: method, get a Google ID token and Google access token from the GIDAuthentication object and exchange them for a Firebase credential:

func sign(_ signIn: GIDSignIn!, didSignInFor user: GIDGoogleUser!, withError error: Error?) {
  // ...
  if let error = error {
    // ...
    return
  }

  guard let authentication = user.authentication else { return }
  let credential = GoogleAuthProvider.credential(withIDToken: authentication.idToken,
                                                    accessToken: authentication.accessToken)
  // ...
}

- (void)signIn:(GIDSignIn *)signIn
didSignInForUser:(GIDGoogleUser *)user
     withError:(NSError *)error {
  // ...
  if (error == nil) {
    GIDAuthentication *authentication = user.authentication;
    FIRAuthCredential *credential =
    [FIRGoogleAuthProvider credentialWithIDToken:authentication.idToken
                                     accessToken:authentication.accessToken];
    // ...
  } else {
    // ...
  }
}

Finally, authenticate with Firebase using the credential:

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
  // ...
}

[[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:.

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

    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.