Link Multiple Auth Providers to an Account in Unity

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.

Firebase.Auth.FirebaseAuth auth = Firebase.Auth.FirebaseAuth.DefaultInstance;

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 Firebase.Auth.FirebaseAuth.SignInAndRetrieveDataWithCredentialAsync methods. For example, get the user's Google ID token, Facebook access token, or email and password.

3. Get a Firebase.Auth.Credential for the new authentication provider:

   Google Sign-In

   Firebase.Auth.Credential credential =
       Firebase.Auth.GoogleAuthProvider.GetCredential(googleIdToken, googleAccessToken);

   Facebook Login

   Firebase.Auth.Credential credential =
       Firebase.Auth.FacebookAuthProvider.GetCredential(accessToken);

   Email-password sign-in

   Firebase.Auth.Credential credential =
       Firebase.Auth.EmailAuthProvider.GetCredential(email, password);

4. Pass the Firebase.Auth.Credential object to the signed-in user's LinkWithCredentialAsync method:

   auth.CurrentUser.LinkWithCredentialAsync(credential).ContinueWith(task => {
     if (task.IsCanceled) {
       Debug.LogError("LinkWithCredentialAsync was canceled.");
       return;
     }
     if (task.IsFaulted) {
       Debug.LogError("LinkWithCredentialAsync encountered an error: " + task.Exception);
       return;
     }
   
     Firebase.Auth.AuthResult result = task.Result;
     Debug.LogFormat("Credentials successfully linked to Firebase user: {0} ({1})",
         result.User.DisplayName, result.User.UserId);
   });

   The call to LinkWithCredentialAsync 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:

   // Gather data for the currently signed in User.
   string currentUserId = auth.CurrentUser.UserId;
   string currentEmail = auth.CurrentUser.Email;
   string currentDisplayName = auth.CurrentUser.DisplayName;
   System.Uri currentPhotoUrl = auth.CurrentUser.PhotoUrl;
   
   // Sign in with the new credentials.
   auth.SignInAndRetrieveDataWithCredentialAsync(credential).ContinueWith(task => {
     if (task.IsCanceled) {
       Debug.LogError("SignInAndRetrieveDataWithCredentialAsync was canceled.");
       return;
     }
     if (task.IsFaulted) {
       Debug.LogError("SignInAndRetrieveDataWithCredentialAsync encountered an error: " + task.Exception);
       return;
     }
   
     Firebase.Auth.AuthResult result = task.Result;
     Debug.LogFormat("User signed in successfully: {0} ({1})",
         result.User.DisplayName, result.User.UserId);
   
     // TODO: Merge app specific details using the newUser and values from the
     // previous user, saved above.
   });

If the call to LinkWithCredentialAsync 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 UnlinkAsync method. You can get the provider IDs of the auth providers linked to a user by calling ProviderData.

// Unlink the sign-in provider from the currently active user.
// providerIdString is a string identifying a provider,
// retrieved via FirebaseAuth.FetchProvidersForEmail().
auth.CurrentUser.UnlinkAsync(providerIdString).ContinueWith(task => {
  if (task.IsCanceled) {
    Debug.LogError("UnlinkAsync was canceled.");
    return;
  }
  if (task.IsFaulted) {
    Debug.LogError("UnlinkAsync encountered an error: " + task.Exception);
    return;
  }

  // The user has been unlinked from the provider.
  Firebase.Auth.AuthResult result = task.Result;
  Debug.LogFormat("Credentials successfully unlinked from user: {0} ({1})",
      result.User.DisplayName, result.User.UserId);
});