[google_sign_in_platform_interface] Add support for serverClientId (flutter#5256)

This PR is a prerequisite for implementing flutter#5250.
It adds support for passing a server client ID to platform implementations when initializing them.

Author: blaugold

packages/google_sign_in/google_sign_in_platform_interface/CHANGELOG.md

@@ -1,3 +1,7 @@
+## 2.2.0
+
+* Adds support for the `serverClientId` parameter.
+
 ## 2.1.3
 
 * Enables mocking models by changing overridden operator == parameter type from `dynamic` to `Object`.

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

@@ -39,6 +39,7 @@ class MethodChannelGoogleSignIn extends GoogleSignInPlatform {
       'scopes': params.scopes,
       'hostedDomain': params.hostedDomain,
       'clientId': params.clientId,
+      'serverClientId': params.serverClientId,
       'forceCodeForRefreshToken': params.forceCodeForRefreshToken,
     });
   }

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

@@ -35,6 +35,7 @@ class SignInInitParameters {
     this.signInOption = SignInOption.standard,
     this.hostedDomain,
     this.clientId,
+    this.serverClientId,
     this.forceCodeForRefreshToken = false,
   });
 
@@ -49,9 +50,30 @@ class SignInInitParameters {
   /// By default, the list of accounts will not be restricted.
   final String? hostedDomain;
 
-  /// The client ID to use when signing in.
+  /// The OAuth client ID of the app.
+  ///
+  /// The default is null, which means that the client ID will be sourced from a
+  /// configuration file, if required on the current platform. A value specified
+  /// here takes precedence over a value specified in a configuration file.
+  /// See also:
+  ///
+  ///   * [Platform Integration](https://github.com/flutter/plugins/tree/main/packages/google_sign_in/google_sign_in#platform-integration),
+  ///     where you can find the details about the configuration files.
   final String? clientId;
 
+  /// The OAuth client ID of the backend server.
+  ///
+  /// The default is null, which means that the server client ID will be sourced
+  /// from a configuration file, if available and supported on the current
+  /// platform. A value specified here takes precedence over a value specified
+  /// in a configuration file.
+  ///
+  /// See also:
+  ///
+  ///   * [Platform Integration](https://github.com/flutter/plugins/tree/main/packages/google_sign_in/google_sign_in#platform-integration),
+  ///     where you can find the details about the configuration files.
+  final String? serverClientId;
+
   /// If true, ensures the authorization code can be exchanged for an access
   /// token.
   ///

packages/google_sign_in/google_sign_in_platform_interface/pubspec.yaml

@@ -4,7 +4,7 @@ repository: https://github.com/flutter/plugins/tree/main/packages/google_sign_in
 issue_tracker: https://github.com/flutter/flutter/issues?q=is%3Aissue+is%3Aopen+label%3A%22p%3A+google_sign_in%22
 # NOTE: We strongly prefer non-breaking changes, even at the expense of a
 # less-clean API. See https://flutter.dev/go/platform-interface-breaking-changes
-version: 2.1.3
+version: 2.2.0
 
 environment:
   sdk: ">=2.12.0 <3.0.0"

packages/google_sign_in/google_sign_in_platform_interface/test/method_channel_google_sign_in_test.dart

@@ -107,6 +107,7 @@ void main() {
           'scopes': <String>['two', 'scopes'],
           'signInOption': 'SignInOption.games',
           'clientId': 'fakeClientId',
+          'serverClientId': null,
           'forceCodeForRefreshToken': false,
         }),
         () {
@@ -144,13 +145,15 @@ void main() {
           scopes: <String>['two', 'scopes'],
           signInOption: SignInOption.games,
           clientId: 'fakeClientId',
+          serverClientId: 'fakeServerClientId',
           forceCodeForRefreshToken: true));
       expect(log, <Matcher>[
         isMethodCall('init', arguments: <String, dynamic>{
           'hostedDomain': 'example.com',
           'scopes': <String>['two', 'scopes'],
           'signInOption': 'SignInOption.games',
           'clientId': 'fakeClientId',
+          'serverClientId': 'fakeServerClientId',
           'forceCodeForRefreshToken': true,
         }),
       ]);