code: def _python_psk_client_callback(ssl_id, hint):
      
      if ssl_id not in _callbacks:
          return ("", "")
      else:
          res = _callbacks[ssl_id](hint)
          return res if isinstance(res, tuple) else (res, "")
docs: Called by _sslpsk.c to return the (psk, identity) tuple for the socket with
      the specified ssl socket.