Took another look at your question:
Your exact needs aren’t clear and I don’t understand Discourse that well, but from what it seems, you need to remix Discourse logic to censor posts based on WeChat’s API. A plugin should be able to do that, if you’re able to get the required WeChat openid, token etc to make the API call (as shown in the docs, API is possible with plain HTTP).
There is discussion here: Do you have any plan developing a plugin of "Sign in with WeChat"? which notes caveats like WeChat not exposing email.
If you want to write a Discourse plugin, tutorials are available on this site.
PS. If you’re having trouble understanding what help you need, I suggest you post on a WeChat developer forum.