code: protected UnixUserGroupInformation getUGI(HttpServletRequest request) {
      String ugi = request.getParameter("ugi");
      try {
        return new UnixUserGroupInformation(ugi.split(","));
      }
      catch(Exception e) {
        LOG.warn("Invalid ugi (= " + ugi + ")");
      }
      return JspHelper.webUGI;
    }
docs: Get {@link UserGroupInformation} from request