code: private void configureIdentityManager(URL undertowResource) {
          try {
              Properties props = new Properties();
              try (InputStream is = undertowResource.openStream()) {
                  props.load(is);
              }
              Map<String, String> config = new LinkedHashMap<>();
              for (Map.Entry<Object, Object> entry : props.entrySet()) {
                  config.put(entry.getKey().toString(), entry.getValue().toString());
              }
              identityManager = (IdentityManager)createConfigurationObject(config, "identityManager");
  
  //            String listeners = config.get("listeners");
  //            if (listeners != null) {
  //                String[] names = listeners.split("(, )+");
  //                for (String name : names) {
  //                    String type = config.get("listeners." + name + ".type");
  //                    String address = config.get("listeners." + name + ".address");
  //                    String port = config.get("listeners." + name + ".port");
  //                    if ("http".equals(type)) {
  //                        builder.addHttpListener(Integer.parseInt(port), address);
  //                    }
  //                }
  //            }
          } catch (Exception e) {
              LOG.error("Exception while starting Undertow", e);
              throw new RuntimeException("Exception while starting Undertow", e);
          }
      }
docs: Loads additional properties and configure {@link ServerControllerImpl#identityManager}
  @param undertowResource