def extract_signed_data(data, extra):
    """Filters out non-white-listed items from the ``extra`` dictionary given.

    :param dict data:
    :param list extra:
    :return dict:
    """
    extracted_extra = dict(data)
    for key, value in data.items():
        if key not in extra:
            extracted_extra.pop(key)
    return extracted_extra
