C# to Teamcity NTLM Authentication failing

Question

I'm unable to authenticate with Teamcity from C# with NTLM. It works in the browser and with Postman.

With logging turned on it seems to do the NTLM handshake, but then settles on a 401 error with:

The token supplied to the function is invalid
To login manually go to "/login.html" page       

Sample code is below. I'm not sure what's wrong here. It works with Basic authentication and a modified URI including httpAuth.

        string uri = "http://teamcityserver/ntlmAuth/action.html?add2Queue=SomeBuild";

        CredentialCache cc = new CredentialCache();
        cc.Add(new Uri(uri), "NTLM", new NetworkCredential("user", "password")); // Have also tried default credentials

        var req = HttpWebRequest.Create(uri);
        req.Method = "POST";
        req.Credentials = cc;
        req.Headers.Add("Origin: http://teamcity");

Answer 1

Got it! The missing factor was that the cookies were not being sent by the client during the NTLM back-and-forth.

Adding this fixed it:

req.CookieContainer = new CookieContainer();