code:   public void init(FilterConfig conf) throws ServletException {
      if (conf != null && "zookeeper".equals(conf.getInitParameter("signer.secret.provider"))) {
        SolrZkClient zkClient =
            (SolrZkClient)conf.getServletContext().getAttribute(KerberosPlugin.DELEGATION_TOKEN_ZK_CLIENT);
        try {
          conf.getServletContext().setAttribute("signer.secret.provider.zookeeper.curator.client",
              getCuratorClient(zkClient));
        } catch (InterruptedException | KeeperException e) {
          throw new ServletException(e);
        }
      }
      super.init(conf);
    }
  
    /**
     * Return the ProxyUser Configuration.  FilterConfig properties beginning with
     * "solr.impersonator.user.name" will be added to the configuration.
     */
    @Override
  