code: public void subscribe(Reference reference) {
  		getResourceFactory()
  				.getApiResource(
  						"/subscription/" + reference.toURLFragment(false))
  				.entity(new Empty(), MediaType.APPLICATION_JSON_TYPE).post();
  	}
docs: Subscribes the user to the given object. Based on the object type, the
  user will receive notifications when actions are performed on the object.
  See the area for more details.
  
  @param reference
  The reference to the object to subscribe to