How to have multiple providers for one account? – Flutter

Introduce the problem

I use an email to log in.

If I log out and try to log in to the same email using Google, the UID of the account changes. I can’t change back to the old UID. How can I provide multiple providers for an account?

What I tried

I asked this question to ChatGPT but it didn’t answer my question. I also googled this problem.

I have read this documentation and used its code, but it didn’t work. Not sure if I’m using its code correctly.

I’ve read this question but it didn’t help me.

A minimal, reproducible example

Future<void> signInWithEmailAndPassword(String email, String password) async {
  try {
    await firebaseAuth.signInWithEmailAndPassword(email: email, password: password);
    final credential = EmailAuthProvider.credential(email: email, password: password);
    await FirebaseAuth.instance.currentUser?.linkWithCredential(credential);
  } on FirebaseAuthException catch (e) {
    throw FirebaseAuthException(code: e.code, message: e.message);
  }
}