Sharing Keycloak users database with Spring Boot resource server

I would like to use Keycloak with a spring boot resource server.
I would like to have endpoints which return the users data. For example getting the users email from the Authentication object, and then getting the users posts etc. or their first login date or things of this nature.

Would it be concidered bad practice to use the same table for keycloak's users and "my" users data?

If it is, how should I approach this problem.
Should I just save the users data into a separate table / database on the first login?

I would appreciate any advice if my approach is wrong in any way

I tried doing some research on this topic but didn't find questions in this topic. Just some ones related to connecting a database to Keycloak.

Here is what I personally use a guide (this are somehow opinions):

• what is involved in access control and user ID is present in tokens (this includes roles, permissions, OpenID claims like name or e-mail, etc., but also access data like 1st and last login). Main reason is performance: this require a round-trip to database only for each token issuance, which should be much less frequent than security rules evaluation
  • if the data is already in Keycloak, then built-in mappers should be enough (look into "mappers" configuration, which is accessible in "Clients -> {client-ID} -> client scopes" tab in latest versions
  • if the data is hosted by another service, then I create a custom mapper with a REST client (sample in this project)
• what is related to domain is spread across resource servers (user "posts" in your listing)

Serving data contained in access tokens from Spring resource server

You can define a @RestController endpoint like this one:

@GetMapping("me")
@PreAuthorize("isAuthenticated()")
public Map<String, Object> getMe(JwtAuthenticationToken auth) {
    return auth.getTokenAttributes();
}