code: public boolean cancelSignatureRequest(String id) throws HelloSignException {
          String url = BASE_URI + SIGNATURE_REQUEST_CANCEL_URI + "/" + id;
          return HttpURLConnection.HTTP_OK == httpClient.withAuth(auth).post(url).asHttpCode();
      }
docs: Cancels an existing signature request. If it has been completed, it will
  delete the signature request from your account.
  
  @param id SignatureRequest id
  @return boolean true if successful
  @throws HelloSignException thrown if there's a problem processing the
  HTTP request or the JSON response.