As we transition to the new Hyland Community, some post links may be temporarily disrupted as we finalize redirects. We apologize for the inconvenience and are working to resolve this as quickly as possible. Details.
The share (client) web app does not pay attention to the X-Alfresco-Remote-User HTTP header. Only the alfresco (server) web app.Share will pay attention to HttpServletRequest.getRemoteUser() i.e. the REMOTE_USER CGI variable.