code: @GET
      @Timed
      @JSONP(callback = "callback", queryParam = "callback")
      @Produces({ MediaType.APPLICATION_JSON,
          MediaTypeAdditional.APPLICATION_JAVASCRIPT })
      @CacheControl(mustRevalidate = true, noCache = true, noStore = true)
      public Id getIdAsJSON(
              @HeaderParam(HttpHeaders.USER_AGENT) final String agent) {
          return new Id(getId(agent));
      }
docs: Get a new ID as JSON
  
  @param agent
  User Agent
  @return generated ID