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:
- Sign in the user using any authentication provider or method.
- 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. Get a
FIRAuthCredential
for the new authentication provider:Google Sign-In
Objective-C
GIDAuthentication *authentication = user.authentication; FIRAuthCredential *credential = [FIRGoogleAuthProvider credentialWithIDToken:authentication.idToken accessToken:authentication.accessToken];
Swift
let authentication = user.authentication let credential = FIRGoogleAuthProvider.credentialWithIDToken(authentication.idToken, accessToken: authentication.accessToken)
Facebook Login
Objective-C
FIRAuthCredential *credential = [FIRFacebookAuthProvider credentialWithAccessToken: [FBSDKAccessToken currentAccessToken].tokenString];
Swift
let credential = FIRFacebookAuthProvider.credentialWithAccessToken(FBSDKAccessToken.currentAccessToken().tokenString)
Email-password sign-in
Objective-C
FIRAuthCredential *credential = [FIREmailPasswordAuthProvider credentialWithEmail:email password:password];
Swift
let credential = FIREmailPasswordAuthProvider.credentialWithEmail(email, password: password)
Pass the
FIRAuthCredential
object to the signed-in user'slinkWithCredential:completion:
method:Objective-C
[[[FIRAuth auth].currentUser] linkWithCredential:credential completion:^(FIRUser *_Nullable user, NSError *_Nullable error) { // ... }];
Swift
FIRAuth.auth()?.currentUser.linkWithCredential(credential) { (user, error) in // ... }
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:Objective-C
FIRUser *prevUser = [FIRAuth auth].currentUser; [[FIRAuth auth] signInWithCredential:credential completion:^(FIRUser *user, NSError *error) { // ... }]; FIRUser *currentUser = [FIRAuth auth].currentUser; // Merge prevUser and currentUser accounts and data // ...
Swift
let prevUser = FIRAuth.auth()?.currentUser FIRAuth.auth()?.signInWithCredential(credential) { (user, error) in // ... } let currentUser = FIRAuth.auth()?.currentUser // 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
unlinkFromProvider:completion:
method. You can get the provider IDs
of the auth providers linked to a user from the providerData
property.
Objective-C
FIRUser *currentUser = [FIRAuth auth].currentUser; [currentUser unlinkFromProvider:providerId completion:^(FIRUser *user, NSError *error) { if (error == nil) { // Provider unlinked from account } }];
Swift
FIRAuth.auth()?.currentUser?.unlinkFromProvider(providerId) { user, error in if let error = error { // ... } else { // Provider unlinked from account } }