public Task<string> SendPost(string cookie, Dictionary<string, string> urlEncodedData, string uri)
{
var stringData = string.Join("&", urlEncodedData.Select(kvp => string.Format("{0}={1}", kvp.Key, kvp.Value)));
return SendPost(cookie, Encoding.UTF8.GetBytes(stringData), uri, "application/x-www-form-urlencoded");
}