def _default_key_normalizer(key_class, request_context):
    """
    Create a pool key of type ``key_class`` for a request.

    According to RFC 3986, both the scheme and host are case-insensitive.
    Therefore, this function normalizes both before constructing the pool
    key for an HTTPS request. If you wish to change this behaviour, provide
    alternate callables to ``key_fn_by_scheme``.

    :param key_class:
        The class to use when constructing the key. This should be a namedtuple
        with the ``scheme`` and ``host`` keys at a minimum.

    :param request_context:
        A dictionary-like object that contain the context for a request.
        It should contain a key for each field in the :class:`HTTPPoolKey`
    """
    context = {}
    for key in key_class._fields:
        context[key] = request_context.get(key)
    context['scheme'] = context['scheme'].lower()
    context['host'] = context['host'].lower()
    return key_class(**context)
