Edit: Keycloak is licensed with the Apache 2.0 license, so none of this is relevant for Keycloak.
GPL is only a problem if you import or change the source code. If you just run it in the backend, as a service, you're most likely fine.
If you customise Keycloak through code, you're probably in GPL violation territory. With the customisability of Keycloak, I doubt that this is something many projects will ever run into.
