Hi Andreas,
Can you please explain what you are trying to achieve in more detail? Are you trying to extend the authentication procedure for the Camunda web application or for a custom application?
While HttpBasicAuthenticationProvider is a REST API class and mentioned in the documentation. EngineRequestAuthorizer is an internal class of the Camunda webapps that in combination with org.camunda.bpm.webapp.impl.security.auth.AuthenticationFilter implements session-based authentication. It is not supposed to be reused in custom projects, however there is also no reason why you should not do it. I assume you are missing the latter class as a servlet filter since it calls the method Authentications#setCurrent.
Cheers,
Thorben