public static void GetTemporaryMedia(string appId, string appSecret, string media_id, Stream stream)
{
var url = string.Format("http://file.api.weixin.qq.com/cgi-bin/media/get?access_token={0}&media_id={1}", AccessToken.GetToken(appId, appSecret), media_id);
WechatWebClient.Download(url, stream);
}