SignInUtility.dart

import 'package:firebase_auth/firebase_auth.dart';
import 'package:flutter/services.dart';
import 'package:google_sign_in/google_sign_in.dart';

class SignInUtility {
  static final FirebaseAuth _auth = FirebaseAuth.instance;
  static final GoogleSignIn googleSignIn = GoogleSignIn();

  static Future<FirebaseUser> signInWithGoogle() async {
    final GoogleSignInAccount googleSignInAccount = await googleSignIn.signIn();

    if (googleSignInAccount == null) {
      // Sign in flow canceled.
      return null;
    }

    final GoogleSignInAuthentication googleSignInAuthentication = await googleSignInAccount.authentication;

    final AuthCredential credential = GoogleAuthProvider.getCredential(
      accessToken: googleSignInAuthentication.accessToken,
      idToken: googleSignInAuthentication.idToken,
    );

    final AuthResult authResult = await _auth.signInWithCredential(credential);
    final FirebaseUser user = authResult.user;

    assert(!user.isAnonymous);
    assert(await user.getIdToken() != null);

    final FirebaseUser currentUser = await _auth.currentUser();
    assert(user.uid == currentUser.uid);

    print("Sign in completed. Welcome ${user.displayName}");

    return user;
  }

  static signOutGoogle() async {
    await googleSignIn.signOut();
    return null;
  }
}