I have to write something like userinfo endpoint in OIDC. I have an user id that I send to userinfo endpoint and here is the problem. I don't have any User entity and any DbContext for Users. I should work on abstractions of User entity and User DbContext because I want all customers to be able to create their own entities. How can I do it? I don't have any ideas, but know that's possible because IdentityServe4 have similar mechanism. I read it source code but it didn't help me.