Consumir un WebService con autenticación básica desde .NET

El título describe bastante bien lo que vamos a solucionar en este post.

public class SecureWebService : ThirdPartyWebService
{
    protected override WebRequest GetWebRequest(Uri uri)
    {
        HttpWebRequest webRequest = (HttpWebRequest)base.GetWebRequest(uri);
        NetworkCredential credentials = Credentials as NetworkCredential;
        if (credentials != null)
        {
            string authInfo =
            ((credentials.Domain != null) && (credentials.Domain.Length > 0) ?
            credentials.Domain + @"\" : string.Empty) +
            credentials.UserName + ":" + credentials.Password;
            authInfo = Convert.ToBase64String(Encoding.Default.GetBytes(authInfo));
            webRequest.Headers["Authorization"] = "Basic " + authInfo;
        }
        return webRequest;
    }
}

via.

Basic Authentication en HTTP Post

string uri = string.Empty, user = string.Empty, password = string.Empty, postData = string.Empty, responseData = string.Empty;
            string encodedAuthorization = Convert.ToBase64String(System.Text.Encoding.UTF8.GetBytes(user + ":" + password));
HttpWebRequest webRequest = WebRequest.Create(uri) as HttpWebRequest;
webRequest.Method = "POST";
webRequest.ContentType = "application/x-www-form-urlencoded";
webRequest.Headers = new WebHeaderCollection();
webRequest.Headers.Add("Authorization: Basic "+encodedAuthorization);

using (StreamWriter rw = new StreamWriter(webRequest.GetRequestStream()))
{
            rw.Write(postData);
}

using (StreamReader sr = new StreamReader(webRequest.GetResponse().GetResponseStream()))
{
            responseData = sr.ReadToEnd();
}