code: def auth_provider_add_user(self, auth_provider_id, username):
          
          url = "/auth_providers/{}/affiliates/{}/dds_user/".format(auth_provider_id, username)
          return self._post(url, {})
docs: Transform an institutional affiliates UID, such as a Duke NetID, to a DDS specific user identity;
          can be used by clients prior to calling DDS APIs that require a DDS user in the request payload.
          Returns user details. Can be safely called multiple times.
          :param auth_provider_id: str: auth provider who supports user adding
          :param username: str: netid we wish to register with DukeDS
          :return: requests.Response containing the successful result