[keycloak-user] Getting user information for a service behind a reverse proxy running keycloak

Hi, Quick question. I have an Apache httpd server running the OIDC httpd adapter. This httpd server acts a reverse proxy to another Tomcat server running legacy JSF code (httpServletRequest). What would be the correct (and simplest) way of getting the user information from within that tomcat scope? (I've tried request.getUserPrincipal() but got a null value). I would appreciate any help! Omri.