I also did not want to use YAML for that but I'm not sure how to modify my existing SQLite User DB to be used by RBAC.

For another app I already started before I knew about RBAC, I already created a 3 level approach: A User has one or more groups (== roles) and each group has one or more permissions.

What I started to do in that app was asking whether a user has a certain permission. So the groups (or roles) are unimportant. Just the permissions they give to the user are important.

The problem I face is: How does RBAC interact with my DB and what is required in the DB to interact properly.

I looked into RBAC because I want to "do it properly" now for the current App I have to work on.