code: public Principal getUserPrincipal()
      {
          LoginHandler lh = Handlers.get( getServletContext() ).getLoginHandler();
          return lh.getUserPrincipal(getHandlerContext());
      }
docs: Get the current logged-in user.  Goes through a custom {@link LoginHandler}, if one has been configured in
  beehive-netui-config.xml.
  
  @return the current logged-in <code>Principal</code>, or <code>null</code> if there is no logged-in user.