1. Apply for registration of WeChat open platform open.weixin.qq.com
2. Bind the official account or applet to the WeChat open platform
3. For WeChat official account, use WeChat webpage authorization to obtain unionid
https://mp.weixin.qq.com/wiki?t=resource/res_main&id=mp1421140842
4. For small programs, there are several ways to obtain unionid
https://developers.weixin.qq.com/miniprogram/dev/api/unionID.html
The decryption example of the first method obtained by the applet refers to the processing method of the Danxi Sports applet
Note: unionid is the id generated by the same user using different products under the WeChat platform, which is used to distinguish users across products.