Application credentials are not supported (or they shouldn't) and the documentation should mention that and we should also mention that only horizon is supported (no CLIs at all) until the RFEs are implemented.

https://docs.redhat.com/en/documentation/red_hat_openstack_platform/17.1/html/integrating_openstack_identity_with_external_user_management_services/assembly_federation-using-rhosp-and-keycloak