docs: def _fetch_transfer_spec(self, node_action, token, bucket_name, paths):
          ''' make hhtp call to Aspera to fetch back trasnfer spec '''
          aspera_access_key, aspera_secret_key, ats_endpoint = self._get_aspera_metadata(bucket_name)
  
          _headers = {'accept': "application/json",
                      'Content-Type': "application/json"}
  
          credentials = {'type': 'token',
                         'token': {'delegated_refresh_token': token}}
  
          _url = ats_endpoint
          _headers['X-Aspera-Storage-Credentials'] = json.dumps(credentials)
          _data = {'transfer_requests': [
                  {'transfer_request': {'paths': paths, 'tags': {'aspera': {
                   'node': {'storage_credentials': credentials}}}}}]}
  
          _session = requests.Session()
          _response = _session.post(url=_url + "/files/" + node_action,
                                    auth=(aspera_access_key, aspera_secret_key),
                                    headers=_headers, json=_data, verify=self._config.verify_ssl)
          return _response