Created [signIn] methos

lib/src/App.dart

@@ -100,4 +100,4 @@ class App extends StatelessWidget {
       ),
     );
   }
-} */
+}

lib/src/resources/google_login_provider.dart

@@ -1 +1,28 @@
+import 'dart:async';
+
 import 'package:firebase_auth/firebase_auth.dart';
+import 'package:google_sign_in/google_sign_in.dart';
+
+class GoogleSignInProvider {
+  final GoogleSignIn _googleSignIn;
+  final FirebaseAuth _auth;
+
+  GoogleSignInProvider([GoogleSignIn googleSignIn, FirebaseAuth firebaseAuth])
+      : _googleSignIn = googleSignIn ?? GoogleSignIn(),
+        _auth = firebaseAuth ?? FirebaseAuth.instance;
+
+  Future<FirebaseUser> signIn() async {
+    final GoogleSignInAccount googleUser = await _googleSignIn.signIn();
+    final GoogleSignInAuthentication googleAuth =
+        await googleUser.authentication;
+
+    final AuthCredential credential = GoogleAuthProvider.getCredential(
+      accessToken: googleAuth.accessToken,
+      idToken: googleAuth.idToken,
+    );
+
+    final FirebaseUser user = await _auth.signInWithCredential(credential);
+    print("signed in " + user.displayName);
+    return user;
+  }
+}