public override byte[] GetPreloadedEntityBody()
{
if (_formValues == null)
return base.GetPreloadedEntityBody();
var sb = new StringBuilder();
foreach (string key in _formValues)
sb.AppendFormat("{0}={1}&", HttpUtility.UrlEncode(key), HttpUtility.UrlEncode(_formValues[key]));
return Encoding.UTF8.GetBytes(sb.ToString());
}