Connect over company proxy with user name

I am trying to connect to external IP address but I am behind company firewall, so I need to connect over the proxy.

I run a test with curl:

curl -v https://IP_ADDRESS_OF_EXTERNAL_CLIENT:6125 -x http://MyComparyProxyAddress.com:8080 -U MYUSERNAME:MYPASSWORD

but I am failing to replicate aforementioned cUrl command in C#:

private static Socket CreateTunnelThruProxy(string destIP, int destPort)
        {
            string destUriWithPort = $"{destIP}:{destPort}";
            UriBuilder uriBuilder = new UriBuilder(destUriWithPort);
            Uri destUri = uriBuilder.Uri;

            var proxy = new WebProxy("http://MyComparyProxyAddress.com", 8080);
            proxy.UseDefaultCredentials = false;
            proxy.Credentials = new NetworkCredential("MYUSERNAME", "MYPASSWORD");
            WebRequest.DefaultWebProxy = proxy;

            IWebProxy webProxy = WebRequest.DefaultWebProxy;

            try
            {
                if (webProxy.IsBypassed(destUri))
                    return null;
            }
            catch (PlatformNotSupportedException)
            {
                // .NET Core doesn't support IWebProxy.IsBypassed
                // (because .NET Core doesn't have access to Windows-specific services, of course)
                return null;
            }

            Uri proxyUri = webProxy.GetProxy(destUri);
            if (proxyUri == null)
                return null;

            IPAddress[] proxyEntry = Dns.GetHostAddresses(proxyUri.Host);
            int iPort = proxyUri.Port;
            IPAddress address = proxyEntry.First(a => a.AddressFamily == AddressFamily.InterNetwork);
            IPEndPoint proxyEndPoint = new IPEndPoint(address, iPort);
            Socket socketThruProxy = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
            socketThruProxy.Connect(proxyEndPoint);

            string proxyMsg = $"CONNECT {destIP}:{destPort} HTTP/1.1 \n\n";
            byte[] buffer = Encoding.ASCII.GetBytes(proxyMsg);
            byte[] buffer12 = new byte[50000];
            socketThruProxy.Send(buffer, buffer.Length, 0);
            int msg = socketThruProxy.Receive(buffer12, 50000, 0);
            string data;
            data = Encoding.ASCII.GetString(buffer12);
            int index = data.IndexOf("200");

            if (index < 0)
                throw new ApplicationException(
                    $"Connection failed to {destUriWithPort} through proxy server {proxyUri.ToString()}.");

            return socketThruProxy;
        }

I keep getting following information from my company proxy:

HTTP/1.1 407 Proxy Authentication Required
Proxy-Authenticate: NEGOTIATE
Proxy-Authenticate: NTLM
Proxy-Authenticate: BASIC realm="ztb"
Cache-Control: no-cache
Pragma: no-cache
Content-Type: text/html; charset=utf-8
Proxy-Connection: close
Connection: close
Content-Length: 797

<HTML><HEAD>
<TITLE>Access Denied</TITLE>
</HEAD>
<BODY>
<body bgcolor="#FFFFEA">
<blockquote>
<TABLE border=0 cellPadding=1 width="80%">
<TR><TD>
<FONT face="Verdana">
<big>Access Denied (authentication_failed)</big>
<BR>
<BR>
</FONT>
</TD></TR>
<TR><TD>
<FONT face="Verdana">
Your credentials could not be authenticated: "Credentials are missing.". You will not be permitted access until your credentials can be verified.
</FONT>
</TD></TR>
<TR><TD>
<FONT face="Verdana">
This is typically caused by an incorrect username and/or password, but could also be caused by network problems.
</FONT>
</TD></TR>
<TR><TD>
<FONT face="Verdana" SIZE=2>
<BR>
For assistance, contact your Tech Desk . PXFFM25
</FONT>
</TD></TR>
</TABLE>
</blockquote>
</FONT>
</BODY></HTML>

I can clearly see that webProxy object contains credentials set by me, the same credentials that are working with cUrl.

Also I am getting the same error when trying simply calling:

IWebProxy webProxy = WebRequest.GetSystemWebProxy();

instead of setting credentials manually, as per code snippet above. So it looks like my credentials are not taken into account....

Any ideas ?

Solution

This can be accomplished in the following way:

 if (IsProxyProvided(settings))
            {
                IPAddress[] proxyEntry = Dns.GetHostAddresses(settings.ProxyHost);
                IPAddress address = proxyEntry.First(a => a.AddressFamily == AddressFamily.InterNetwork);
                IPEndPoint proxyEndPoint = new IPEndPoint(address, settings.ProxyPort);
                socket.Connect(proxyEndPoint);

                if (AreProxyCredntialsProvided(settings))
                {
                    var basicAuthBase64 = Convert.ToBase64String(
                        Encoding.GetEncoding("ISO-8859-1").GetBytes($"{settings.ProxyUserName}:{settings.ProxyUserNamePassword}"));
                    var proxyMessage = $"Proxy-Authorization: {string.Format("Basic {0}", basicAuthBase64)} \r\n";
                    var keepAlive = "Connection: keep-alive\r\n";
                    var request = $"CONNECT {endpoint.Address}:{endpoint.Port} HTTP/1.1 \r\n" + proxyMessage + keepAlive + "\r\n";
                    byte[] buffer = Encoding.ASCII.GetBytes(request);
                    socket.Send(buffer, buffer.Length, 0);
                }
            }

Thanks to Victor Victor Stone who had similar issue here