参考资料
Flutter Google Sign In

环境介绍

系统：Windows 10
IDE：Android Studio 3.5.2
Flutter：1.22.2
Dart：2.8.4
Gradle：5.6.2

插件

1. google_sign_in
2. firebase_auth

平台

Android

1. 前往Firebase创建项目
2. 侧边栏进入build -> Authentication -> Sign-in method，开启Google项
3. 侧边栏进入 Project Overview ，创建APP
4. 进入APP设置，填写基本信息
5. 使用keytool创建keystore，并获取SHA-1、SHA-256，并填写到对应APP信息中
6. 下载google-services.json放入android/app/
7. 配置OAuth同意屏
8. 配置android/build.gradle

   buildscript{
   	...
   	repositories{
       	maven { url 'https://maven.aliyun.com/repository/google' }
       	maven { url 'https://maven.aliyun.com/repository/jcenter' }
       	maven { url 'http://maven.aliyun.com/nexus/content/groups/public' }
   	}
   	dependencies{
   		...
       	classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
       	classpath 'com.google.gms:google-services:4.3.3'
   	}
   }
   ...
   allprojects{
   	repositories{
       	maven { url 'https://maven.aliyun.com/repository/google' }
       	maven { url 'https://maven.aliyun.com/repository/jcenter' }
       	maven { url 'http://maven.aliyun.com/nexus/content/groups/public' }
   	}
   }
   

9. 配置android/app/build.gradle

   dependencies{
       implementation 'com.google.firebase:firebase-analytics:17.2.2'
   }
   apply plugin: 'com.google.gms.google-services'
   

10. 编写代码

    // 要求的 google token scope
    final GoogleSignIn _googleSignIn = GoogleSignIn(
      scopes: <String>[
        'email',
        'profile',
      ],
    );
    // 谷歌登陆
    Future _loginForGoogle(BuildContext context) async {
      await _googleSignIn.signOut();
    
      GoogleSignInAccount _currentUser = await _googleSignIn.signIn();
      GoogleSignInAuthentication gSA = await _currentUser.authentication;
    
      var id = _currentUser.id;
    
      // 需要发送给后端的accessToken
      String accessToken = gSA.accessToken;
      
      // ...继续操作
    }
    

IOS

待补充