[google_sign_in] Redesign API for current identity SDKs - Platform Implementations (#9479)

This is the platform implementation portion of #9267

Part of flutter/flutter#119300

## Pre-Review Checklist

[^1]: Regular contributors who have demonstrated familiarity with the repository guidelines only need to comment if the PR is not auto-exempted by repo tooling.

Author: stuartmorgan-g

packages/google_sign_in/google_sign_in_android/CHANGELOG.md

@@ -1,5 +1,9 @@
-## NEXT
+## 7.0.0
 
+* **BREAKING CHANGE**: Switches to implementing version 3.0 of the platform
+  interface package, rather than 2.x, significantly changing the API surface.
+* Switches to Sign in with Google (`CredentialManager`) as the underlying
+  SDK, removing usage of the deprecated Google Sign In for Android SDK.
 * Updates minimum supported SDK version to Flutter 3.27/Dart 3.6.
 
 ## 6.2.1

packages/google_sign_in/google_sign_in_android/README.md

@@ -13,3 +13,25 @@ should add it to your `pubspec.yaml` as usual.
 
 [1]: https://pub.dev/packages/google_sign_in
 [2]: https://flutter.dev/to/endorsed-federated-plugin
+
+## Integration
+
+To use Google Sign-In, you'll need to register your application, either
+[using Firebase](https://firebase.google.com/docs/android/setup), or
+[directly with Google Cloud Platform](https://developer.android.com/identity/sign-in/credential-manager-siwg#set-google).
+
+* If you are use the `google-services.json` file and Gradle-based registration
+  system, no identifiers need to be provided in Dart when initializing the
+  `GoogleSignIn` instance when running on Android.
+* If you are not using `google-services.json`, you need to pass the client
+  ID of the *web* application you registered as the `serverClientId` when
+  initializing the `GoogleSignIn` instance.
+
+If you encounter `APIException` errors, double-check that you have followed all
+of the registration steps in the instructions above.
+
+You will also need to enable any OAuth APIs that you want, using the
+[Google Cloud Platform API manager](https://console.developers.google.com/). For
+example, if you want to mimic the behavior of the Google Sign-In example app,
+you'll need to enable the
+[Google People API](https://developers.google.com/people/).

packages/google_sign_in/google_sign_in_android/android/build.gradle

@@ -2,13 +2,15 @@ group 'io.flutter.plugins.googlesignin'
 version '1.0-SNAPSHOT'
 
 buildscript {
+    ext.kotlin_version = '2.1.10'
     repositories {
         google()
         mavenCentral()
     }
 
     dependencies {
         classpath 'com.android.tools.build:gradle:8.5.0'
+        classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
     }
 }
 
@@ -20,6 +22,7 @@ rootProject.allprojects {
 }
 
 apply plugin: 'com.android.library'
+apply plugin: 'kotlin-android'
 
 android {
     namespace 'io.flutter.plugins.googlesignin'
@@ -35,6 +38,14 @@ android {
         targetCompatibility JavaVersion.VERSION_11
     }
 
+    kotlinOptions {
+        jvmTarget = '11'
+    }
+
+    sourceSets {
+        main.java.srcDirs += 'src/main/kotlin'
+    }
+
     lintOptions {
         checkAllWarnings true
         warningsAsErrors true
@@ -56,7 +67,10 @@ android {
 }
 
 dependencies {
-    implementation 'com.google.android.gms:play-services-auth:21.0.0'
+    implementation 'androidx.credentials:credentials:1.5.0'
+    implementation 'androidx.credentials:credentials-play-services-auth:1.5.0'
+    implementation 'com.google.android.libraries.identity.googleid:googleid:1.1.1'
+    implementation 'com.google.android.gms:play-services-auth:21.3.0'
     testImplementation 'junit:junit:4.13.2'
     testImplementation 'org.mockito:mockito-inline:5.2.0'
 }