At https://github.com/ONLYOFFICE/ControlPanel/issues/6 I showed my findings in how to use KeyCloak as a provider. If somebody else could also test it, then maybe this can be prepared to be used in the documentation. I can provide screenshots and everything, but best not to base it on one experience.
And please no vague scripts and info on installing Keycloak, as was done with Shibboleth. The current docs on SAML were actually counter-productive.