docs: protected String getCurrentTheme() {
          val request = WebUtils.getHttpServletRequestFromExternalWebflowContext();
          if (request != null) {
              val session = request.getSession(false);
              val paramName = casProperties.getTheme().getParamName();
              if (session != null) {
                  return (String) session.getAttribute(paramName);
              }
              return (String) request.getAttribute(paramName);
          }
          return null;
      }