code: @Override
      public void sessionCreated(NextFilter nextFilter, IoSession session)
              throws Exception {
          for (Map.Entry<String, Object> e : attributes.entrySet()) {
              session.setAttribute(e.getKey(), e.getValue());
          }
  
          nextFilter.sessionCreated(session);
      }
docs: Puts all pre-configured attributes into the actual session attribute
  map and forward the event to the next filter.