RememberMe Java Client

I‘m fairly new to Keycloak but I think it‘s the greatest thing I‘ve seen after other products.

I spent a lot of time building a working prototype with Grails and Java Spring Boot. Both are working, but there‘s one thing that is very unclear to me:

My java clients should remember the logged in user after successfully authenticate the user in Keycloak. Right now, it seems that Spring Security stores the information (is it the token?) in the JSESSIONID. This gets destroyed every time I close the browser.

What‘s the magic to keep the user within Spring Security logged in also after a browser restart?

The rememberMe function on Keycloak Realm works differently, as far as I can see?