code: public FutureData<IdentityList> list(String label, int page, int perPage) {
          FutureData<IdentityList> future = new FutureData<>();
          ParamBuilder b = newParams();
          if (label != null) {
              b.put("label", label);
          }
          if (page > 0) {
              b.put("page", page);
          }
          if (perPage > 0) {
              b.put("per_page", perPage);
          }
          URI uri = b.forURL(config.newAPIEndpointURI(IDENTITY));
          Request request = config.http().
                  GET(uri, new PageReader(newRequestCallback(future, new IdentityList(), config)));
          performRequest(future, request);
          return future;
      }
docs: /*
  List identities with a given label and page details
  
  @param label   which label you'd like to list (can be null)
  @param page    page number (can be 0)
  @param perPage items per page (can be 0)
  @return List of identities