def get_confirm_token(session, url):
    """
    Google may include a confirm dialog if the file is too big. This retreives the
    confirmation token and uses it to complete the download.

    :param aiohttp.ClientSession session: used to the get the cookies from the reponse
    :param str url : the url is used to filter out the correct cookies from the session
    :return the cookie if found or None if not found
    :rtype str
    """
    cookies = session.cookie_jar.filter_cookies(url)
    for key, cookie in cookies.items():
        if key.startswith('download_warning'):
            return cookie
    return None