Add some changes to platform interface

packages/google_sign_in/google_sign_in_platform_interface/lib/google_sign_in_platform_interface.dart

@@ -10,6 +10,23 @@ import 'method_channel_google_sign_in.dart';
 
 enum SignInOption { standard, games }
 
+class GoogleSignInUserData {
+  GoogleSignInUserData({
+    this.displayName, this.email, this.id, this.photoUrl, this.idToken
+  });
+  String displayName;
+  String email;
+  String id;
+  String photoUrl;
+  String idToken;
+}
+
+class GoogleSignInTokenData {
+  GoogleSignInTokenData({this.idToken, this.accessToken});
+  String idToken;
+  String accessToken;
+}
+
 /// The interface that implementations of google_sign_in must implement.
 ///
 /// Platform implementations that live in a separate package should extend this
@@ -32,15 +49,15 @@ abstract class GoogleSignInPlatform {
     throw UnimplementedError('init() has not been implemented.');
   }
 
-  Future<Map<String, dynamic>> signInSilently() async {
+  Future<GoogleSignInUserData> signInSilently() async {
     throw UnimplementedError('signInSilently() has not been implemented.');
   }
 
-  Future<Map<String, dynamic>> signIn() async {
+  Future<GoogleSignInUserData> signIn() async {
     throw UnimplementedError('signIn() has not been implemented.');
   }
 
-  Future<Map<String, String>> getTokens() async {
+  Future<GoogleSignInTokenData> getTokens({@required String email, bool shouldRecoverAuth}) async {
     throw UnimplementedError('getTokens() has not been implemented.');
   }
 
@@ -56,7 +73,7 @@ abstract class GoogleSignInPlatform {
     throw UnimplementedError('isSignedIn() has not been implemented.');
   }
 
-  Future<void> clearAuthCache() async {
+  Future<void> clearAuthCache({@required String token}) async {
     throw UnimplementedError('clearAuthCache() has not been implemented.');
   }
 }

packages/google_sign_in/google_sign_in_platform_interface/lib/method_channel_google_sign_in.dart

@@ -8,6 +8,7 @@ import 'package:flutter/services.dart';
 import 'package:meta/meta.dart' show required;
 
 import 'google_sign_in_platform_interface.dart';
+import 'src/utils.dart';
 
 const MethodChannel _channel = MethodChannel('plugins.flutter.io/google_sign_in');
 
@@ -23,23 +24,27 @@ class MethodChannelGoogleSignIn extends GoogleSignInPlatform {
   }
 
   @override
-  Future<Map<String, dynamic>> signInSilently() async {
-    return _channel.invokeMapMethod<String, dynamic>('signInSilently');
+  Future<GoogleSignInUserData> signInSilently() async {
+    return _channel.invokeMapMethod<String, dynamic>('signInSilently').then(
+      (Map<String, dynamic> data) => nativeUserDataToPluginUserData(data));
   }
 
   @override
-  Future<Map<String, dynamic>> signIn() async {
-    return _channel.invokeMapMethod<String, dynamic>('signIn');
+  Future<GoogleSignInUserData> signIn() async {
+    return _channel.invokeMapMethod<String, dynamic>('signIn').then(
+      (Map<String, dynamic> data) => nativeUserDataToPluginUserData(data));
   }
 
   @override
-  Future<Map<String, String>> getTokens({String email, bool shouldRecoverAuth = true}) async {
+  Future<GoogleSignInTokenData> getTokens({String email, bool shouldRecoverAuth = true}) async {
     return _channel.invokeMapMethod<String, dynamic>(
       'getTokens',
       <String, dynamic>{
         'email': email,
         'shouldRecoverAuth': shouldRecoverAuth,
-      });
+      }).then(
+        (Map<String, dynamic> data) => nativeTokenDataToPluginTokenData(data)
+      );
   }
 
   @override

packages/google_sign_in/google_sign_in_platform_interface/lib/src/utils.dart

@@ -0,0 +1,24 @@
+import '../google_sign_in_platform_interface.dart';
+
+GoogleSignInUserData nativeUserDataToPluginUserData(Map<String, dynamic> data) {
+  if (data == null) {
+    return null;
+  }
+  return GoogleSignInUserData(
+    displayName: data['displayName'],
+    email: data['email'],
+    id: data['id'],
+    photoUrl: data['photoUrl'],
+    idToken: data['idToken'] 
+  );
+}
+
+GoogleSignInTokenData nativeTokenDataToPluginTokenData(Map<String, dynamic> data) {
+  if (data == null) {
+    return null;
+  }
+  return GoogleSignInTokenData(
+    idToken: data['idToken'],
+    accessToken: data['accessToken'],
+  );
+}