signInWithCredential method

Future<UserCredential?> signInWithCredential(AuthCredential credential)

SignIn with Credential to Firebase

Implementation

Future<UserCredential?> signInWithCredential(
    AuthCredential credential) async {
  try {
    //sign-in with provided credential to firebase
    return await auth.signInWithCredential(credential);

    //firebase auth exception
  } on FirebaseAuthException catch (e) {
    //check if user tried to provide already signed in user with different third party login system
    //for e.g if user signed in with google and that credential is saved in firebase
    //and user tries to sign in with facebook with the same email
    //firebase throws account exists with different credential
    //to solve this we need to link those accounts in to one
    if (e.code == 'account-exists-with-different-credential') {
      // get email from exception
      String email = e.email!;

      //get pending credential from exception
      AuthCredential pendingCredential = e.credential!;

      //get sign-in methods from exception
      List<String> userSignInMethods =
          await auth.fetchSignInMethodsForEmail(email);

      //check in which sign-in method user signed in first
      if (userSignInMethods.first == "google.com") {
        //sign with credential with found credential
        ThirdPartyLoginWithGoogle thirdPartyLoginWithGoogle =
            ThirdPartyLoginWithGoogle();
        var userCredential =
            await thirdPartyLoginWithGoogle.signInWithGoogle();

        //link pending credential with previous one
        return await linkProviders(userCredential!, pendingCredential);
      }

      if (userSignInMethods.first == "facebook.com") {
        //sign with credential with found credential
        ThirdPartyLoginWithGoogle thirdPartyLoginWithGoogle =
            ThirdPartyLoginWithGoogle();
        var userCredential =
            await thirdPartyLoginWithGoogle.signInWithGoogle();

        //link pending credential with previous one
        return await linkProviders(userCredential!, pendingCredential);
      }
    } else {
      rethrow;
    }
  }
  return null;
}