微信unionid机制
UnionID 机制说明:https://developers.weixin.qq.com/miniprogram/dev/framework/open-ability/union-id.html
获取微信公众号用户的基本信息(UnionID机制):https://www.cnblogs.com/microtiger/p/10007892.html
微信网页开发之获取用户unionID的两种方法--基于微信的多点登录用户识别:https://www.cnblogs.com/yangtoude/p/multi-site-login-based-on-wechat.html
用户没有关注公众号是否能获取到UnionId ?:
https://developers.weixin.qq.com/community/develop/doc/000a420bbe82f0a24229ec36456c00
App授权登录和公众号获取的unionid不一样?:https://developers.weixin.qq.com/community/develop/doc/000a646b310ce8026c194d3335b800