加载登陆按钮时， 会立即检查授权 情况, 如果成功 the Google servers return an access token and pass a new authorization result object to the callback. 如果该按钮无法进行即时模式授权，则用户必须单击登录按钮以触发访问流程
To enable cross-platform single sign-on:
- The Android and web app must be registered in the same Google API Console project.
- The requested scopes on each platform must match the scopes from other platforms.
关联 app 和 web site
https://developers.google.com/identity/smartlock-passwords/android/associate-apps-and-sites