Maybe we got lucky with the configuration but we use the approach documented for the keycloak-saml-adapter with Jetty as the app server.

There is still a lot work done to ensure keys are generated in the proper locations and that necessary product id values (corresponds to SAML SP entityID) are generated.

In short, it is not a simple plug-n-play, lots of hacking to get the result we needed but the adapter itself does what it needs to do.