// Key values
    const string XAuthUsername = "x_auth_username";
    const string XAuthPassword = "x_auth_password";
    const string XAuthMode = "x_auth_mode";

    public bool GetAccessToken(string userName, string password)
        {

            List<KeyValuePair<string, string>> para = new List<KeyValuePair<string, string>>();
            para.Add(new KeyValuePair<string, string>(XAuthUsername, userName));
            para.Add(new KeyValuePair<string, string>(XAuthPassword, UrlEncode(password, Encoding.Default, true)));
            para.Add(new KeyValuePair<string, string>(XAuthMode, "client_auth"));

            var target = CreateUrl(XAuthProviderAccessTokenUrl, RequestMethod.POST, para);
            try
            {
                var ret = Http.WebConnectDownloadString(new Uri(target), "POST", null);
                if (ret.Exception != null)
                    throw ret.Exception;
                if (!ret.Succeeded)
                {
                    return false;
                }
                var rd = SplitParamDict(ret.Data);
                if (rd.ContainsKey("oauth_token") && rd.ContainsKey("oauth_token_secret"))
                {
                    Token = rd["oauth_token"];
                    Secret = rd["oauth_token_secret"];
                    return true;
                }
                else
                {
                    return false;
                }
            }
            catch (WebException)
            {
                throw;
            }
        }