vkontakte redirect authorization. See https://vk.com/developers.php?oid=-1&p=%D0%90%D0%B2%D1%82%D0%BE%D1%80%D0%B8%D0%B7%D0%B0%D1%86%D0%B8%D1%8F_%D1%81%D0%B0%D0%B9%D1%82%D0%BE%D0%B2