keycloak: Keycloak Authz Client 19.0.2 is not backward compatible with Keycloak 18 and earlier

Describe the bug

Hi everyone, we are seeing a few reports in Quarkus, most recently captured in https://github.com/quarkusio/quarkus/discussions/28649#discussioncomment-3900729, suggesting that using quarkus-keycloak-authorization depending on KC 19.0.2 libraries does not work if it is used against KC 18 or earlier.

Version

18

Expected behavior

No response

Actual behavior

No response

How to Reproduce?

Run Keycloak Authz Client 19.0.2 against Keycloak 18

Anything else?

No response