code: public static IPrincipalToLocal GetPrincipalToLocalPlugin(Map storm_conf) {
          IPrincipalToLocal ptol = null;
          try {
              String ptol_klassName = (String) storm_conf.get(Config.STORM_PRINCIPAL_TO_LOCAL_PLUGIN);
              Class klass = Class.forName(ptol_klassName);
              ptol = (IPrincipalToLocal) klass.newInstance();
              ptol.prepare(storm_conf);
          } catch (Exception e) {
              throw new RuntimeException(e);
          }
          return ptol;
      }
docs: Construct a principal to local plugin
  
  @param conf storm configuration
  @return the plugin