<%@ Page Language="C#" %>
<%@ Import Namespace="System.Text" %>
<%@ Import Namespace="System.Net" %>
<%@ Import Namespace="System.IO" %>
<script runat="server">

    protected void Page_Load(object sender, EventArgs e)
    {
        string username = "";
        string password = "";

        string postData = "PHP_AUTH_USER=" + username;
        postData += ("&PHP_AUTH_PW=" + password);
        byte[] data = System.Text.Encoding.UTF8.GetBytes(postData);

        CookieContainer cc = new CookieContainer();//you need
        HttpWebRequest myRequest =
          (HttpWebRequest)WebRequest.Create("your url here");

        myRequest.Accept = "*/*";//You don't need this, but just in case :)
        myRequest.Method = "POST";
        myRequest.UserAgent = (string)Request.Browser.Capabilities[""];
        myRequest.ContentType = "application/x-www-form-urlencoded";
        myRequest.ContentLength = data.Length;
        myRequest.CookieContainer = cc;//You need

        Stream newStream = myRequest.GetRequestStream();

        newStream.Write(data, 0, data.Length);
        newStream.Close();

        using (WebResponse wr = myRequest.GetResponse())
        {
            if (((HttpWebResponse)wr).StatusCode == HttpStatusCode.OK)
            {
                using (newStream = wr.GetResponseStream())
                {
                    using (StreamReader reader = new StreamReader(newStream))
                    {
                        Response.ClearContent();
                        Response.Write(reader.ReadToEnd());
                    }
                }
            }
        }
    }
</script>