code: def load_or_create_client_key(pem_path):
      
      acme_key_file = pem_path.asTextMode().child(u'client.key')
      if acme_key_file.exists():
          key = serialization.load_pem_private_key(
              acme_key_file.getContent(),
              password=None,
              backend=default_backend())
      else:
          key = generate_private_key(u'rsa')
          acme_key_file.setContent(
              key.private_bytes(
                  encoding=serialization.Encoding.PEM,
                  format=serialization.PrivateFormat.TraditionalOpenSSL,
                  encryption_algorithm=serialization.NoEncryption()))
      return JWKRSA(key=key)
docs: Load the client key from a directory, creating it if it does not exist.
  
      .. note:: The client key that will be created will be a 2048-bit RSA key.
  
      :type pem_path: ``twisted.python.filepath.FilePath``
      :param pem_path: The certificate directory
          to use, as with the endpoint.