c# - HttpClient and using proxy - constantly getting 407

Question

Here is the code:

 HttpClient client = null;
 HttpClientHandler httpClientHandler = new HttpClientHandler()
 {
    Proxy = new WebProxy(string.Format("{0}:{1}", proxyServerSettings.Address, 
    proxyServerSettings.Port),false),
    PreAuthenticate = true,
    UseDefaultCredentials = false,
 };


 this.httpClientHandler.Credentials = new NetworkCredential(proxyServerSettings.UserName, 
                        proxyServerSettings.Password);


 this.client = new HttpClient(this.httpClientHandler);

And when I finally do this:

HttpResponseMessage httpResponseMessage = this.client.PostAsync(urlToPost, new StringContent(data, Encoding.UTF8, this.mediaType)).Result;

It always throws the

The remote server returned an error: (407) Proxy Authentication Required.

Which I do not understand for the world of me.

The same proxy set up works just fine when is configured in IE10 or if I use the HttpWebRequest class instead

Answer 1

You're setting the proxy credentials in the wrong place.

httpClientHandler.Credentials are the credentials you give to the server after the proxy has already established a connection. If you get these wrong, you'll probably get a 401 or 403 response.

You need to set the credentials given to the proxy, or it will refuse to connect you to the server in the first place. The credentials you provide to the proxy may be different from the ones you provide to the server. If you get these wrong, you'll get a 407 response. You're getting a 407 because you never set these at all.

// First create a proxy object
var proxy = new WebProxy
{
    Address = new Uri($"http://{proxyHost}:{proxyPort}"),
    BypassProxyOnLocal = false,
    UseDefaultCredentials = false,

    // *** These creds are given to the proxy server, not the web server ***
    Credentials = new NetworkCredential(
        userName: proxyUserName,
        password: proxyPassword)
};

// Now create a client handler which uses that proxy
var httpClientHandler = new HttpClientHandler
{
    Proxy = proxy,
};

// Omit this part if you don't need to authenticate with the web server:
if (needServerAuthentication)
{
    httpClientHandler.PreAuthenticate = true;
    httpClientHandler.UseDefaultCredentials = false;

    // *** These creds are given to the web server, not the proxy server ***
    httpClientHandler.Credentials = new NetworkCredential(
        userName: serverUserName,
        password: serverPassword);
}

// Finally, create the HTTP client object
var client = new HttpClient(handler: httpClientHandler, disposeHandler: true);