Flutter How to Link Multiple Auth Providers to an Firebase Account? - firebase

Question

I am using firebase in my flutter application. In my app user can sign in or register using 3 ways.
Email id and password.
Google
Facebook.
This is my Firebase setting.
This is my user collection.
Now my doubt is that how do I link multiple auth providers for a user having same email id ?
I am storing user's info into User collection with Uid. If I enable multiple account to multiple providers how can I store user's data in same document ?
I have search a lot on google but didn't find proper solution.
For registration with email ID I am using this.
final newUser = await _auth.createUserWithEmailAndPassword(
email: widget.email, password: widget.pass);
Then I am storing user's data into User collection. (In this I have one more form, from where I am getting other data).
Google sign in code
Future<User> signInWithGoogle() async {
// Trigger the authentication flow
final GoogleSignInAccount googleUser = await _googleSignIn.signIn();
// Obtain the auth details from the request
final GoogleSignInAuthentication googleAuth = await googleUser.authentication;
// Create a new credential
final GoogleAuthCredential credential = GoogleAuthProvider.credential(
accessToken: googleAuth.accessToken,
idToken: googleAuth.idToken,
);
// Once signed in, return the UserCredential
final UserCredential authResult = await _firebaseAuth.signInWithCredential(credential);
final User user = authResult.user;
print('authResult');
print(authResult);
return user;
}

Answer 1

Users are actually allowed to sign in to your app using multiple authentication providers by linking auth provider credentials to an existing user account.
You can follow the documentation here for the process of linking auth provider credentials to an existing user account:
I suggest to also visit the official documentation of Firebase for Flutter.