code: public JSONObject post(String path, JSONObject content, Map<String,String> headers)
              throws ServiceException, JSONException {
          String sub = getSegment(path, 4);
          if ("event".equals(sub)) {
              SlackEvent event = new SlackEvent(content);
              EventHandler eventHandler = getEventHandler(event.getType(), event);
              if (eventHandler == null) {
                  throw new ServiceException("Unsupported handler type: " + event.getType()
                          + (event.getChannel() == null ? "" : (":" + event.getChannel())));
              }
              return eventHandler.handleEvent(event);
          } else {
              // action/options request
              SlackRequest request = new SlackRequest(content);
              String userId = getAuthUser(headers);
              // TODO: ability to map request.getUser() to corresponding MDW user
              String callbackId = request.getCallbackId();
              if (callbackId != null) {
                  int underscore = callbackId.lastIndexOf('_');
                  if (underscore > 0) {
                      String handlerType = callbackId.substring(0, underscore);
                      String id = callbackId.substring(callbackId.lastIndexOf('/') + 1);
                      ActionHandler actionHandler = getActionHandler(handlerType, userId, id,
                              request);
                      if (actionHandler == null)
                          throw new ServiceException("Unsupported handler type: " + handlerType);
  
                      return actionHandler.handleRequest(userId, id, request);
                  }
              }
              throw new ServiceException(ServiceException.BAD_REQUEST, "Bad or missing callback_id");
          }
      }
docs: Responds to requests from Slack.