I would be interested to know why you are creating new API keys… using an API key. It seems a little circular, and I wonder if we can come up with a better solution for your problem?
I have created a new user via API. (with admin API and KEY)
now I need to post a post or topic for this user.
But seems no API for me to do that… So I think maybe I should create a API for this user, then I switch my header with this new API… then I can make a post or topic on behalf of this new user…
Rather than creating a key for each user, you can use an “all users” key, then change the Api-Username header on the request. There is an example at the top of https://docs.discourse.org/