How to obtain the refreshToken when google sign in with Flutter / Firebase - flutter

Question

I've already did the google sign with the firebase flutter toolkit. When sign in is done, I receive the idToken to read/write on the database.
final FirebaseAuth _auth = FirebaseAuth.instance;
final GoogleSignIn googleSignIn = GoogleSignIn();
Future<String> signInWithGoogle() async {
await Firebase.initializeApp();
final GoogleSignInAccount googleSignInAccount = await googleSignIn.signIn();
final GoogleSignInAuthentication googleSignInAuthentication = await googleSignInAccount.authentication;
final AuthCredential credential = GoogleAuthProvider.credential(
accessToken: googleSignInAuthentication.accessToken,
idToken: googleSignInAuthentication.idToken,
);
final UserCredential authResult = await _auth.signInWithCredential(credential);
final User user = authResult.user;
final idToken = await user.getIdToken();
}
The problem is, I need to auto login user when he opens the app again. So, when I sign in with google, I do not receive the refresh token, needed to get the new valid idToken, as the Doc.
How can I get the refreshToken ?

Answer 1

You can use SharedPreferences to set a bool value when a user is logged in from google and check the value when the app restarts. Don't forget to remove this value from shared preferences when user logged out.

Answer 2

I'm pretty sure googl_sign_in keeps the refresh token internally and you always receive a valid idToken. If it's about to expire, you can force renewal.
Answering your direct question about refreshToken:
You can create your own implementation of the google_sign_in class. In the end it's just an OAuth token. Here's a web implementation of a custom google_sign_in service: https://stackoverflow.com/a/69746036/5492496
I'm pretty sure you can do the same for Android & iOS using web view, you will loose the single click functionality on Android though.