firebase-auth-2-google-sign-in-step-3-4.dart

  //Create Google Auth credentials to pass to Firebase
  final GoogleAuthCredential googleAuthCredential =
  GoogleAuthProvider.credential(
    accessToken: googleAuth.accessToken,
    idToken: googleAuth.idToken,
  );

  //Authenticate against Firebase with Google credentials
  await firebaseAuth.signInWithCredential(googleAuthCredential).then((userCredential) => {
    setState(() => {
      user = userCredential
    })
  });
}