title: Flutter Google-SignIn via Flutter idToken issues
body: <p>I am trying to get an idToken from my client Flutter app to send back to my backend for verification, the problem is I either don't get the idToken but rather an "instanceOfGetIDToken" or something along those lines or it spits out a token that does not have anything to do with the Firebase app it's linked to, I'm quite confused since the user appears in the Firebase console for the app but the consent screen mentions the idNumber instead of the name and when I check the JWT it has somewhat okay information but the issuer and everything is different?</p>
  
  <pre><code>final GoogleSignIn _googleSignIn = GoogleSignIn();
  final FirebaseAuth _auth = FirebaseAuth.instance;
  Future&lt;FirebaseUser&gt; _handleSignIn() async {
    final GoogleSignInAccount googleUser = await _googleSignIn.signIn();
    final GoogleSignInAuthentication googleAuth = await googleUser.authentication;
  
    final AuthCredential credential = GoogleAuthProvider.getCredential(
      idToken: googleAuth.idToken,
    );
  
    final FirebaseUser user = (await _auth.signInWithCredential(credential)).user;
    print(credential);
    return user;
  }
  </code></pre>