code: def from_url(cls, reactor, url, key, alg=RS256, jws_client=None):
          
          action = LOG_ACME_CONSUME_DIRECTORY(
              url=url, key_type=key.typ, alg=alg.name)
          with action.context():
              check_directory_url_type(url)
              jws_client = _default_client(jws_client, reactor, key, alg)
              return (
                  DeferredContext(jws_client.get(url.asText()))
                  .addCallback(json_content)
                  .addCallback(messages.Directory.from_json)
                  .addCallback(
                      tap(lambda d: action.add_success_fields(directory=d)))
                  .addCallback(cls, reactor, key, jws_client)
                  .addActionFinish())
docs: Construct a client from an ACME directory at a given URL.
  
          :param url: The ``twisted.python.url.URL`` to fetch the directory from.
              See `txacme.urls` for constants for various well-known public
              directories.
          :param reactor: The Twisted reactor to use.
          :param ~josepy.jwk.JWK key: The client key to use.
          :param alg: The signing algorithm to use.  Needs to be compatible with
              the type of key used.
          :param JWSClient jws_client: The underlying client to use, or ``None``
              to construct one.
  
          :return: The constructed client.
          :rtype: Deferred[`Client`]