How to ignore a certificate error with c# 2.0 WebClient - without the certificate

Question

Using Visual Studio 2005 - C# 2.0, System.Net.WebClient.UploadData(Uri address, byte[] data) Windows Server 2003

So here's a stripped down version of the code:

static string SO_method(String fullRequestString)
{
    string theUriStringToUse = @"https://10.10.10.10:443"; // populated with real endpoint IP:port
    string proxyAddressAndPort = @"http://10.10.10.10:80/"; // populated with a real proxy IP:port
    Byte[] utf8EncodedResponse; // for the return data in utf8
    string responseString; // for the return data in utf16

    WebClient myWebClient = new WebClient(); // instantiate a web client
    WebProxy proxyObject = new WebProxy(proxyAddressAndPort, true);// instantiate & popuylate a web proxy
    myWebClient.Proxy = proxyObject; // add the proxy to the client
    myWebClient.Headers.Add("Content-Type", "application/x-www-form-urlencoded"); // stick some stuff in the header

    UTF8Encoding utf8Encoding = new UTF8Encoding(false);// create a utf8 encoding
    Byte[] utf8EncodedRequest = HttpUtility.UrlEncodeToBytes(fullRequestString, utf8Encoding); // convert the request data to a utf8 byte array

    try
    {
        utf8EncodedResponse = myWebClient.UploadData(theUriStringToUse, "POST", utf8EncodedRequest); // pass the utf8-encoded byte array
        responseString = utf8Encoding.GetString(utf8EncodedResponse); // get a useable string out of the response
    }
    catch (Exception e)
    {
        // some other error handling
        responseString = "";// show the basics of the problem
    }
    return responseString;// return whatever ya got
}

This is the error I get:

The underlying connection was closed: Could not establish trust relationship for the SSL/TLS secure channel.

I don't have much control to see what's happening when the request goes out. I'm told that it's reaching the correct destination and there's a "certificate error". This is supposedly because there's a literal mismatch between the IP address in my request and the URL it resolves to. I have more than one IP I'm supposed to round-robin to so specifying the URL won't work. I'm not attaching a certificate - nor am I supposed to according to the endpoint owners. Per "them" the certificate error is 'normal and I am supposed to ignore it.

The cert in question is supposedly one of the many verisign certs that is "just there" on our server. The examples I've seen for ignoring cert errors all seem to imply that the requestor is attaching a specific x509 certificate (which I'm not).

I looked over .net WebService, bypass ssl validation! which kinda-sorta describes my problem - except it also kinda-sorta doesn't because I don't know which certificate (if any) I should reference.

Is there a way for me to ignore the error without actually knowing/caring what certificate is causing the problem?

and please - kid gloves, small words, and "for dummies" code as I'm not exactly a heavy hitter.
This traffic is over a private line - so my understanding is that ignoring the cert error is not as big a deal as if it were open internet traffic.

user_98491 · Answer

I wanted to disable SSL verification for a specific domain without globally deactivating it because there might be other requests running which should not be affected, so I came up with this solution (please note that uri is a variable inside a class:

        private byte[] UploadValues(string method, NameValueCollection data)
        {
            var client = new WebClient();

            try
            {
                ServicePointManager.ServerCertificateValidationCallback +=
                    ServerCertificateValidation;

                returnrclient.UploadValues(uri, method, parameters);

            }
            finally
            {
                ServicePointManager.ServerCertificateValidationCallback -=
                    ServerCertificateValidation;
            }
        }

        private bool ServerCertificateValidation(object sender,
            X509Certificate certificate, X509Chain chain,
            SslPolicyErrors sslPolicyErrors)
        {
            var request = sender as HttpWebRequest;
            if (request != null && request.Address.Host.Equals(
                this.uri.Host, StringComparison.OrdinalIgnoreCase))
                return true;
            return false;
        }

How to ignore a certificate error with c# 2.0 WebClient - without the certificate

6 Answers