Login user programatically from Java

Hi, in our application we create user account when user buys a subscription, we do it using org.keycloak.admin.client.Keycloak. I’m able to create user without any problem.

App is in Java, secured by Tomcat Keycloak Adapter.

My qustion is, is there a way that I can login user as next step, from java, without user interaction? I know how to login user using REST call, but how can I make tomcat adapter think that user is logged in? Somehow pass user token there?

I tried AuthzClient module of Keycloak but I think it’s not meant to be use for my case.

Any ideas will be much appreciated.
Thanks in advance.
Mariusz