Obtain a new token by refresh token with google_sign_in Flutter

I'm writing an application that call google fit rest api from Flutter.

I need to sign with google using (https://pub.dev/packages/google_sign_in). I can obtain a token without problem (see Did anyone manage to get the id token from google sign in (Flutter)) but how to obtain a new token when it is expired?

I dont' want to ask to the user to login and obtain a new token every hour

You can do this in 2 ways.

1. You can use the API.

2. I don't know if this is standard but you can do a silent login every time the user opens the app, the silent log logs into the user account without user interaction and this way you have a new token. Like this:

import 'package:google_sign_in/google_sign_in.dart';
 // you may only login with google, delete hide part if not
import 'package:firebase_auth/firebase_auth.dart' hide EmailAuthProvider; 

//...

Future<void> silentSignIn() async {
    try {
      final GoogleSignIn googleSignIn = GoogleSignIn();
      final GoogleSignInAccount? googleUser =
          await googleSignIn.signInSilently();  // silent login
      if (googleUser != null) {
        final GoogleSignInAuthentication googleAuth =
            await googleUser.authentication;
        final AuthCredential credential = GoogleAuthProvider.credential(
          accessToken: googleAuth.accessToken,
          idToken: googleAuth.idToken,
        );
        await FirebaseAuth.instance.signInWithCredential(credential);
        print('User silently signed in with Google.');
      } else {
        print('No user signed in silently.');
        // Optionally, redirect to a sign-in page
      }
    } catch (e) {
      print('Error during silent sign-in: $e');
      // Handle errors or redirect to a manual sign-in page
    }
  }