I know this is old but in case someone comes across it again, I used these simple snippets:

Code:
private void Authenticate()
{
	var request = WebRequest.Create(_connectionInfo.Url + "/authentication-point/authenticate");
	var auth = Encoding.UTF8.GetBytes(_connectionInfo.Username + ":" + _connectionInfo.Password);
	request.Headers[HttpRequestHeader.Authorization] = "Basic " + Convert.ToBase64String(auth);
...