Get the cookies for the given class.

    We do not validate the cookies if they are loaded from a cookies file
    because this is intended for debugging purposes or if the coursera
    authentication process has changed.

def get_cookies_for_class(session, class_name,
                          cookies_file=None,
                          username=None,
                          password=None):
    """
    Get the cookies for the given class.

    We do not validate the cookies if they are loaded from a cookies file
    because this is intended for debugging purposes or if the coursera
    authentication process has changed.
    """
    if cookies_file:
        cookies = find_cookies_for_class(cookies_file, class_name)
        session.cookies.update(cookies)
        logging.info('Loaded cookies from %s', cookies_file)
    else:
        cookies = get_cookies_from_cache(username)
        session.cookies.update(cookies)
        if validate_cookies(session, class_name):
            logging.info('Already authenticated.')
        else:
            get_authentication_cookies(session, class_name, username, password)
            write_cookies_to_cache(session.cookies, username)