Something we have to fix anyways. Its on my todo list.One problem with this approach is that you end up having a separate JDBC connection and transaction even if it uses the same database the Keycloak server uses.
I'm really not a big fan of this extension and this is something I do not want to support for product ever.Take a look at https://github.com/keycloak/keycloak/tree/master/examples/providers/domain-extension/src/main/java/org/keycloak/examples/domainextension/jpa for example which allows adding custom entities to the main EntityManager.