Ok, I got it by myself.
For everyone coming from google, there is something you must understand. The
documentation assumes you have a new application and want to deploy it with keycloak SSO. the jBPM included business-central.war does not have the login methods to use OIDC - which will be included in wildfly 25 (current wildfly is 23.02). The trick is to have an application that gets a login-session for you with keycloak. This application can you get
here.
BUT: the combination of wildfly23, KIE-SERVER: 7.61.0 (jboss/jbpm-server-full) with the latest keycloak adapter (16.1.0) DOESN'T work. I think the quickstart-application isn't up to date.
My solution was the combination of wildfly19, KIE-SERVER 7.56.0 and keycloak-adapter 14.0.0
Problem here: you have to manually update maven, which ist just a tar.gz DL and setting the right environment variables.
If anyone can explain how I can implement the keycloak mechanism in wildfly23 with keycloak-adapter 16.1.0 I can fix the quickstart-application and append a patch (here and a PR).
Hope someone can help.
Greetings,
Björn