How to config api_url when there is No /userinfo endpoint provided by my Oauth server

Thank torkel,
I’m able to get ALL valid user information from another RESTFUL API, including username, email, etc, and according to the Response of /introspect endpoint mentioned in my question description, the /introspect endpoint can return me the login user’s userName, I’m thinking of writing my own RESTFUL API to return the login user’s information, how do u think about it?

BTW. I’m able to write a restful api to return a fake userinfo, and works well.