import base64


def base64url_decode(data: bytes) -> bytes:
    """
    Decodes a URL Safe Base64 encoded bytes string into its original contents.

    :param data: Data to be decoded.
    :type data: bytes

    :return: Original contents of the provided encoded data.
    :rtype: bytes
    """

    data += b"=" * (len(data) % 4)
    return base64.urlsafe_b64decode(data)