在Android App中集成Google Sign-In。
参考链接：https://developers.google.com/identity/sign-in/android/start-integrating
Google API Console :https://console.developers.google.com

在开始集成之前:

1、你需要配置Google API Console.
2、设置你的Android Studio.

必备条件：

1、android设备需要Android 4.1及以上版本，并且安装Google Play 商店。
或者模拟器Android4.2.2以上版本，Google Play services 版本15.0.0以上
2、最新版本的Android SDK，安装SDK Tools 组件。并且在Android Studio里面配置好SDK。
3、项目编译版本在4.1以上版本。

以下是具体步骤：

一、添加 Google Play services

1、在project build.gradle 文件中, 确认包含 Google's Maven。

allprojects {
    repositories {
        google()

        // If you're using a version of Gradle lower than 4.1, you must instead use:
        // maven {
        //     url 'https://maven.google.com'
        // }
    }
}

2、在app-level build.gradle 文件中, 定义 Google Play services :

apply plugin: 'com.android.application'
    ...

    dependencies {
        implementation 'com.google.android.gms:play-services-auth:17.0.0'
    }

二、配置一个 Google API Console 项目
https://console.developers.google.com/apis/credentials
选择android项目。
添入：SHA1值。
获取SHA1 keytool -keystore shooting.keystore -list -v

三、添加代码
1、在onCreate中添加：

        // Configure sign-in to request the user's ID, email address, and basic
        // profile. ID and basic profile are included in DEFAULT_SIGN_IN.
        GoogleSignInOptions gso = new GoogleSignInOptions.Builder(GoogleSignInOptions.DEFAULT_SIGN_IN)
                .requestEmail()
                .build();
        // Build a GoogleSignInClient with the options specified by gso.
        mGoogleSignInClient = GoogleSignIn.getClient(this, gso);

2、添加cocos可以访问的登录方法：

/////google signin////////
public static void signInByGoogle() {
    Intent signInIntent = AppActivity._instance.mGoogleSignInClient.getSignInIntent();
    AppActivity._instance.startActivityForResult(signInIntent, RC_SIGN_IN);
}

////google sign-in
//在onActivityResult 中获取对象 GoogleSignInAccount 
//After the user signs in, you can get a GoogleSignInAccount object for the user in the activity's onActivityResult method.
@Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        //facebook
        callbackManager.onActivityResult(requestCode, resultCode, data);
        super.onActivityResult(requestCode, resultCode, data);
        SDKWrapper.getInstance().onActivityResult(requestCode, resultCode, data);

        //google sign-in
        // Result returned from launching the Intent from GoogleSignInClient.getSignInIntent(...);
        if (requestCode == RC_SIGN_IN) {
            // The Task returned from this call is always completed, no need to attach
            // a listener.
            Task<GoogleSignInAccount> task = GoogleSignIn.getSignedInAccountFromIntent(data);
            handleSignInResult(task);
        }
    }

    ////google sign-in 
    //The GoogleSignInAccount object contains information about the signed-in user, such as the user's name.
    private void handleSignInResult(@NonNull Task<GoogleSignInAccount> completedTask) {
        Log.d(TAG, "handleSignInResult:" + completedTask.isSuccessful());

        try {
            GoogleSignInAccount account = completedTask.getResult(ApiException.class);
            updateUI(account);

        } catch (ApiException e) {
            Log.w(TAG, "handleSignInResult:error", e);

            // Clear the local account
            mAccount = null;

            // Signed out, show unauthenticated UI.
            updateUI(null);
        }
    }
    ////google sign-in 
    // 更新用户信息
    void updateUI(GoogleSignInAccount account){
        if(account != null){
            // Store the account from the result
            mAccount = account;
            Log.d(TAG, "mAccount:" + mAccount);

            AppActivity._instance.runOnGLThread(new Runnable() {
                public void run(){
                    Cocos2dxJavascriptJavaBridge.evalString("yxl.loginSuccess(\"google"
                            + AppActivity._instance.mAccount.getId()
                            + "\",\""
                            + AppActivity._instance.mAccount.getDisplayName()
                            + "\",\""
                            +AppActivity._instance.mAccount.getPhotoUrl()
                            + "\",\""
                            +AppActivity._instance.displayCountryName
                            +"\");");
                }
            });
        }else{
            Log.d(TAG, "mAccount:null");
        }
    }