import base64


def key64uToKey(key64u):
    """
    key64uToKey allows you to convert a base64 url-file safe key string to a byte string

    :param key64u: base64 ulr-file safe string
    :return: byte string
    """
    if key64u is None:
        return None

    return base64.urlsafe_b64decode(key64u.encode("utf-8"))