code: func (s *APIServer) keepAliveNode(auth ClientI, w http.ResponseWriter, r *http.Request, p httprouter.Params, version string) (interface{}, error) {
  	var handle services.KeepAlive
  	if err := httplib.ReadJSON(r, &handle); err != nil {
  		return nil, trace.Wrap(err)
  	}
  	if err := auth.KeepAliveNode(r.Context(), handle); err != nil {
  		return nil, trace.Wrap(err)
  	}
  	return message("ok"), nil
  }
docs: // keepAliveNode updates node TTL in the backend