最近在升级Google Play Game的unity插件之后，出现登录失败的问题，日志显示需要Web Client ID
07-03 20:19:51.646: D/TokenFragment(3682): Fragment exists.. calling processRequests
07-03 20:19:51.646: D/TokenFragment(3682): Building client for: 4a8416a0 (a:true e:false i:true wc: WEB_CLIENTID f: false)
07-03 20:19:51.646: E/TokenFragment(3682): Web client ID is needed for Auth Code
07-03 20:19:51.646: D/TokenFragment(3682): Done with processRequest, result is pending.
初步怀疑是设置的Web Client ID丢失了，但是检查之后发现并没有丢失，检查代码时发现Assets\GooglePlayGames\GameInfo.cs代码里面的WebClientId和ApplicationId没有设置，当时并没有发现问题，后来查了官方的升级说明(https://github.com/playgameservices/play-games-plugin-for-unity/blob/master/UPGRADING.txt)
）之后，有说明 After upgrading, redo setup (click "Google Play Games | Android Setup" and/or
"Google Play Games | iOS Setup" on the menu). Do this even if you had already done
this before on this project. 做完这一步之后发现GameInfo.cs里面有修改WebClientId和ApplicationId的值，所以大致问题应该就出在这里了，升级之后重新设置一遍
