WebClient and impersonate as other user

Question

I created a web service hosted in SharePoint 2010 and I want to unit test its behaviour/results. Now when I try to run a test with a different user, I always get the results of the previous user and my test fails.

I can see in fiddler that for subsequent requests no authentication is happening: My implementation of the webclient throws away all cookies, so why is there no re-auth? I am passing different credentials to the HttpWebRequest.Credentials property because I use NTLM.

Update 1:

private CookieContainer container = new CookieContainer();

    protected override WebRequest GetWebRequest(Uri address)
    {
        WebRequest request = base.GetWebRequest(address);

        if (request is HttpWebRequest)
        {
            (request as HttpWebRequest).CookieContainer = null;
        }

        return request;
    }

    public string HttpPost(string URI, Dictionary<string, object> data, NetworkCredential credentials)
    {
        HttpWebRequest req = (HttpWebRequest)GetWebRequest(new Uri(URI));

        if (credentials != null)
        {
            req.Credentials = credentials;
            req.UseDefaultCredentials = false;
        }
        else
        {
            req.UseDefaultCredentials = true;
        }

        //Add these, as we're doing a POST
        req.ContentType = "application/json; charset=UTF-8";
        req.Method = "POST";

        this.Encoding = Encoding.UTF8;
        this.Headers.Add(HttpRequestHeader.ContentType, "application/json; charset=UTF-8");
        this.Headers.Add(HttpRequestHeader.CacheControl, "no-cache");
        this.Headers.Add(HttpRequestHeader.Pragma, "no-cache");
        this.Headers.Add(HttpRequestHeader.Accept, "application/json, text/javascript, */*; q=0.01");

        if (data != null)
        {
            string json = JsonConvert.SerializeObject(data, new JsonSerializerSettings()
            {
                DateFormatHandling = DateFormatHandling.MicrosoftDateFormat,
                DateTimeZoneHandling = DateTimeZoneHandling.Local,
                NullValueHandling = NullValueHandling.Ignore,
                ReferenceLoopHandling = ReferenceLoopHandling.Ignore
            });

            byte[] bytes = System.Text.Encoding.ASCII.GetBytes(json);
            req.ContentLength = bytes.Length;
            System.IO.Stream os = req.GetRequestStream();
            os.Write(bytes, 0, bytes.Length); //Push it out there
            os.Close();
        }
        else
        {
            req.ContentLength = 0;
        }



        System.Net.WebResponse resp = req.GetResponse();
        if (resp == null) return null;
        System.IO.StreamReader sr = new System.IO.StreamReader(resp.GetResponseStream());
        return sr.ReadToEnd().Trim();
    }

Answer 1

It somehow started to work after a reboot. The above code should work.