WebRequest SOAP with WSS-PasswordType PasswordText

I need to do a POST to a web service and I can not find the return.

I managed to make the request from the SoapUI app, but when I take that to the ASPNET MVC code in C # I always get the error: "The requested URL was rejected"

Basically I do not know where to configure the security data (username, password and password type, in this case PASSWORDTEXT).

Will you have an example?

I leave what I have armed that I managed to rescue from other examples on the web:

[TestMethod]
public void TestWSFalabella()
{
    var _url = "url";
    var _action = "";

    XmlDocument soapEnvelopeXml = CreateSoapEnvelope();
    HttpWebRequest webRequest = CreateWebRequest(_url, _action);

    string auth = string.Format("Basic {0}", Convert.ToBase64String(System.Text.Encoding.Default.GetBytes(string.Format("{0}:{1}", "usuario", "password"))));
    webRequest.PreAuthenticate = true;
    webRequest.Headers.Add(HttpRequestHeader.Authorization, auth);


    webRequest.UseDefaultCredentials = false;

    InsertSoapEnvelopeIntoWebRequest(soapEnvelopeXml, webRequest);

    // begin async call to web request.
    IAsyncResult asyncResult = webRequest.BeginGetResponse(null, null);

    // suspend this thread until call is complete. You might want to
    // do something usefull here like update your UI.
    asyncResult.AsyncWaitHandle.WaitOne();

    // get the response from the completed web request.
    string soapResult;
    using (WebResponse webResponse = webRequest.EndGetResponse(asyncResult))
    {
        using (StreamReader rd = new StreamReader(webResponse.GetResponseStream()))
        {
            soapResult = rd.ReadToEnd();
        }
        Console.Write(soapResult);
    }
}