Link Multiple Auth Providers to an Account on Apple Platforms

You can allow users to sign in to your app using multiple authentication providers by linking auth provider credentials to an existing user account. Users are identifiable by the same Firebase user ID regardless of the authentication provider they used to sign in. For example, a user who signed in with a password can link a Google account and sign in with either method in the future. Or, an anonymous user can link a Facebook account and then, later, sign in with Facebook to continue using your app.

Before you begin

Add support for two or more authentication providers (possibly including anonymous authentication) to your app.

Link auth provider credentials to a user account

To link auth provider credentials to an existing user account:

1. Sign in the user using any authentication provider or method.
2. Complete the sign-in flow for the new authentication provider up to, but not including, calling one of the FIRAuth.signInWith methods. For example, get the user's Google ID token, Facebook access token, or email and password.

3. Get a FIRAuthCredential for the new authentication provider:

   Google Sign-In

   Swift

   guard
   letauthentication=user?.authentication,
   letidToken=authentication.idToken
   else{
   return
   }
   letcredential=GoogleAuthProvider.credential(withIDToken:idToken,
   accessToken:authentication.accessToken)

   Objective-C

   FIRAuthCredential*credential=
   [FIRGoogleAuthProvidercredentialWithIDToken:result.user.idToken.tokenString
   accessToken:result.user.accessToken.tokenString];

   Facebook Login

   Swift

   letcredential=FacebookAuthProvider
   .credential(withAccessToken:AccessToken.current!.tokenString)

   Objective-C

   FIRAuthCredential*credential=[FIRFacebookAuthProvider
   credentialWithAccessToken:[FBSDKAccessTokencurrentAccessToken].tokenString];

   Email-password sign-in

   Swift

   letcredential=EmailAuthProvider.credential(withEmail:email,password:password)

   Objective-C

   FIRAuthCredential*credential=
   [FIREmailAuthProvidercredentialWithEmail:email
   password:password];

4. Pass the FIRAuthCredential object to the signed-in user's linkWithCredential:completion: method:

   Swift

   user.link(with:credential){authResult,errorin
   // ...
   }
   }

   Objective-C

   [[FIRAuthauth].currentUserlinkWithCredential:credential
   completion:^(FIRAuthDataResult*result,NSError*_Nullableerror){
   // ...
   }];

   The call to linkWithCredential:completion: will fail if the credentials are already linked to another user account. In this situation, you must handle merging the accounts and associated data as appropriate for your app:

   Swift

   letprevUser=Auth.auth().currentUser
   Auth.auth().signIn(with:credential){authResult,errorin
   ifleterror=error{
   letauthError=errorasNSError
   ifisMFAEnabled,authError.code==AuthErrorCode.secondFactorRequired.rawValue{
   // The user is a multi-factor user. Second factor challenge is required.
   letresolver=authError
   .userInfo[AuthErrorUserInfoMultiFactorResolverKey]as!MultiFactorResolver
   vardisplayNameString=""
   fortmpFactorInfoinresolver.hints{
   displayNameString+=tmpFactorInfo.displayName??""
   displayNameString+=" "
   }
   self.showTextInputPrompt(
   withMessage:"Select factor to sign in\n\(displayNameString)",
   completionBlock:{userPressedOK,displayNamein
   varselectedHint:PhoneMultiFactorInfo?
   fortmpFactorInfoinresolver.hints{
   ifdisplayName==tmpFactorInfo.displayName{
   selectedHint=tmpFactorInfoas?PhoneMultiFactorInfo
   }
   }
   PhoneAuthProvider.provider()
   .verifyPhoneNumber(with:selectedHint!,uiDelegate:nil,
   multiFactorSession:resolver
   .session){verificationID,errorin
   iferror!=nil{
   print(
   "Multi factor start sign in failed. Error: \(error.debugDescription)"
   )
   }else{
   self.showTextInputPrompt(
   withMessage:"Verification code for \(selectedHint?.displayName??"")",
   completionBlock:{userPressedOK,verificationCodein
   letcredential:PhoneAuthCredential?=PhoneAuthProvider.provider()
   .credential(withVerificationID:verificationID!,
   verificationCode:verificationCode!)
   letassertion:MultiFactorAssertion?=PhoneMultiFactorGenerator
   .assertion(with:credential!)
   resolver.resolveSignIn(with:assertion!){authResult,errorin
   iferror!=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
   // ...
   }
   // Merge prevUser and currentUser accounts and data
   // ...
   }

   Objective-C

   FIRUser*prevUser=[FIRAuthauth].currentUser;
   [[FIRAuthauth]signInWithCredential:credential
   completion:^(FIRAuthDataResult*_NullableauthResult,
   NSError*_Nullableerror){
   if(isMFAEnabled && error && error.code==FIRAuthErrorCodeSecondFactorRequired){
   FIRMultiFactorResolver*resolver=error.userInfo[FIRAuthErrorUserInfoMultiFactorResolverKey];
   NSMutableString*displayNameString=[NSMutableStringstring];
   for(FIRMultiFactorInfo*tmpFactorInfoinresolver.hints){
   [displayNameStringappendString:tmpFactorInfo.displayName];
   [displayNameStringappendString:@" "];
   }
   [selfshowTextInputPromptWithMessage:[NSStringstringWithFormat:@"Select factor to sign in\n%@",displayNameString]
   completionBlock:^(BOOLuserPressedOK,NSString*_NullabledisplayName){
   FIRPhoneMultiFactorInfo*selectedHint;
   for(FIRMultiFactorInfo*tmpFactorInfoinresolver.hints){
   if([displayNameisEqualToString:tmpFactorInfo.displayName]){
   selectedHint=(FIRPhoneMultiFactorInfo*)tmpFactorInfo;
   }
   }
   [FIRPhoneAuthProvider.provider
   verifyPhoneNumberWithMultiFactorInfo:selectedHint
   UIDelegate:nil
   multiFactorSession:resolver.session
   completion:^(NSString*_NullableverificationID,NSError*_Nullableerror){
   if(error){
   [selfshowMessagePrompt:error.localizedDescription];
   }else{
   [selfshowTextInputPromptWithMessage:[NSStringstringWithFormat:@"Verification code for %@",selectedHint.displayName]
   completionBlock:^(BOOLuserPressedOK,NSString*_NullableverificationCode){
   FIRPhoneAuthCredential*credential=
   [[FIRPhoneAuthProviderprovider]credentialWithVerificationID:verificationID
   verificationCode:verificationCode];
   FIRMultiFactorAssertion*assertion=[FIRPhoneMultiFactorGeneratorassertionWithCredential:credential];
   [resolverresolveSignInWithAssertion:assertioncompletion:^(FIRAuthDataResult*_NullableauthResult,NSError*_Nullableerror){
   if(error){
   [selfshowMessagePrompt:error.localizedDescription];
   }else{
   NSLog(@"Multi factor finanlize sign in succeeded.");
   }
   }];
   }];
   }
   }];
   }];
   }
   elseif(error){
   // ...
   return;
   }
   // User successfully signed in. Get user data from the FIRUser object
   if(authResult==nil){return;}
   FIRUser*user=authResult.user;
   // ...
   }];
   // Merge prevUser and currentUser accounts and data
   // ...
   }];

If the call to linkWithCredential:completion: succeeds, the user can now sign in using any linked authentication provider and access the same Firebase data.

Unlink an auth provider from a user account

You can unlink an auth provider from an account, so that the user can no longer sign in with that provider.

To unlink an auth provider from a user account, pass the provider ID to the unlink method. You can get the provider IDs of the auth providers linked to a user from the providerData property.

Auth.auth().currentUser?.unlink(fromProvider:providerID!){user,errorin
// ...
}

[[FIRAuthauth].currentUserunlinkFromProvider:providerID
completion:^(FIRUser*_Nullableuser,NSError*_Nullableerror){
// ...
}];

Troubleshooting

If you encounter errors when trying to link multiple accounts, see the documentation on verified email addresses.