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I was trying to log in to my WordPress admin panel using C# (WebClient/HttpWebRequest).

I send a POST request to /wp-login.php. It responds with cookies like this:

Set-Cookie: wordpress_26...cf9e; path=/wordpress/wp-content/plugins; httponly
Set-Cookie: wordpress_26...cf9e; path=/wordpress/wp-admin; httponly
Set-Cookie: wordpress_logged_in_26...43b3; path=/wordpress/; httponly

And it also redirects to /wp-admin/: Location: http://109.120.169.99/wordpress/wp-admin/

The problem is that the second cookie (with path=/wp-admin) is not added to CookieContainer, so login fails.

I looked into HttpWebRequest source code and http://referencesource.microsoft.com/#System/net/System/Net/_CookieModule.cs (OnReceiveHeaders) and found out that it uses ResponseUri for all cookies.

I tried to add the cookie manually using response uri and got an exception that path is invalid. After that I found this answer CookieException with CookieContainer: The 'Path' part of the cookie is invalid : it says that the Uri has to match the path from the cookie when adding to CookieContainer.

I ended up disabling AllowAutoRedict (handling it manually) and manually adding these cookies.

Here is my code:

public static void Auth(string url, string username, string password)
{
    var webClient = new CookieAwareWebClient();

    // load page to get some cookies
    string loginPageHtml = webClient.DownloadString(url);

    webClient.Headers.Add(HttpRequestHeader.ContentType, "application/x-www-form-urlencoded");
    webClient.Headers.Add(HttpRequestHeader.Referer, url);

    var postValues = new NameValueCollection()
        {
            {"log", username},
            {"pwd", password},
            {"wp-sumbit", "Log In"},
            {"redirect_to", url.Replace("wp-login.php", "wp-admin/") },
            {"testcookie", "1"}
        };

    webClient.AllowRedirects = false; // to handle cookies and redirect manually

    byte[] response = webClient.UploadValues(url, postValues);
    string html = Encoding.UTF8.GetString(response);

    // <FIX>, handle cookies and redirect manually

    string cookies = webClient.ResponseHeaders[HttpResponseHeader.SetCookie];
    var cookiesArr = cookies.Split(',');

    foreach (var cookieStr in cookiesArr)
    {
        var parts = cookieStr.Split(';').Select(s => s.Trim());

        foreach (var part in parts)
        {
            if (part.Contains("path="))
            {
                string path = part.Replace("path=", "");

                var uri = new Uri(url);

                if (path != "/" && !uri.LocalPath.Contains(path))
                {
                    var uriBuilder = new UriBuilder(uri.Scheme, uri.Host, 80,
                        path);

                    webClient.CookieContainer.SetCookies(uriBuilder.Uri, cookieStr);
                }
            }
        }
    }
    // </FIX>

    while (webClient.StatusCode() == HttpStatusCode.Redirect)
    {
        string redirectUrl = webClient.ResponseHeaders[HttpResponseHeader.Location];

        html = webClient.DownloadString(redirectUrl);
    }

    if (html.Contains("?action=logout"))
        Console.WriteLine("Login success");
    else
        Console.WriteLine("Login fail");
}

WebClient:

// WebClient with CookieContainer
public class CookieAwareWebClient : WebClient
{
    private WebRequest _request = null;
    private WebResponse _response = null;

    public CookieContainer CookieContainer { get; private set; }

    public string UserAgent { get; set; }

    public bool AllowRedirects { get; set; }

    public CookieAwareWebClient()
    {
        UserAgent = "Mozilla/5.0 (Windows NT 6.2; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/29.0.1547.76 Safari/537.36";
        CookieContainer = new CookieContainer();
        AllowRedirects = true;
    }

    protected override WebRequest GetWebRequest(Uri address)
    {
        _request = base.GetWebRequest(address);
        if (_request is HttpWebRequest)
        {
            var httpRequest = (HttpWebRequest)_request;
            httpRequest.CookieContainer = CookieContainer;
            httpRequest.UserAgent = UserAgent;

            httpRequest.AllowAutoRedirect = AllowRedirects;

            httpRequest.ProtocolVersion = HttpVersion.Version11;

            httpRequest.Timeout = 50000;
        }
        return _request;
    }

    protected override WebResponse GetWebResponse(WebRequest request)
    {
        _response = base.GetWebResponse(request);

        return _response;
    }

    // Returns status code of the last response
    public HttpStatusCode StatusCode()
    {
        var httpResponse = _response as HttpWebResponse;

        if (httpResponse == null)
            throw new InvalidOperationException("Unable to retrieve the status code, maybe you have not made a request yet.");

        var result = httpResponse.StatusCode;

        return result;
    }
}

I also tried using .NET 4.5 HttpClient but the same result (I think it uses HttpWebRequest underneath too):

public static void Auth2(string url, string username, string password)
{
    using (var httpClient = new HttpClient())
    {
        var loginPageHtml = httpClient.GetStringAsync(url).Result;

        var postContent = new List<KeyValuePair<string, string>>()
            {
                new KeyValuePair<string, string>("log", username),
                new KeyValuePair<string, string>("pwd", password),
                new KeyValuePair<string, string>("wp-submit", "Log In"),
                new KeyValuePair<string, string>("redirect_to", url.Replace("wp-login.php", "wp-admin/")),
                new KeyValuePair<string, string>("testcookie", "1")
            };

        var response = httpClient.PostAsync(url, new FormUrlEncodedContent(postContent)).Result;

        string html = response.Content.ReadAsStringAsync().Result;

        if (html.Contains("?action=logout"))
            Console.WriteLine("Login success");
        else
            Console.WriteLine("Login fail");
    }
}

Am I doing something wrong or is it a bug in HttpWebRequest/CookieContainer?

Here is the full source code for convenience if someone wants to test it: https://gist.github.com/AlexP11223/5c176972426605ee2112 (my test website and login/password also should work)

And Fiddler logs:

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