I am trying to deploy Keycloak server with a legacy database containing all user and groups data. I have successfully implemented a user federation spi (mostly following the official quickstart and this tutorial) and I can see external users in Keycloak console. I have also implemented getGroupsInternal() method from AbstractUserAdapterFederatedStorage class to fetch groups from external storage. When I open details of a (federated) user in the console, I can see a list of groups this user belongs to. However, when I try to create new group-based policy, I don't see any groups there and there isn't an option to freely type group name either. Which methods/classes/interfaces do I need to implement in order to make this happen?
I am quite new to Keycloak, so in general what is the best way to figure out which methods/classes/interfaces need to be implemented for a specific functionality? For example, in my question above I found the functionality I want in the admin console, what is the best way to find out which methods/classes exactly need to be implemented based on the functionality in the UI?