WebApi HttpClient not sending client certificate

There are 2 types of certificates. The first is the public .cer file that is sent to you from the owner of the server. This file is just a long string of characters. The second is the keystore certificate, this is the selfsigned cert you create and send the cer file to the server you are calling and they install it. Depending on how much security you have, you might need to add one or both of these to the Client (Handler in your case). I’ve only seen the keystore cert used on one server where security is VERY secure. This code gets both certificates from the bin/deployed folder:

#region certificate Add
                // KeyStore is our self signed cert
                // TrustStore is cer file sent to you.

                // Get the path where the cert files are stored (this should handle running in debug mode in Visual Studio and deployed code) -- Not tested with deployed code
                string executableLocation = Path.GetDirectoryName(AppDomain.CurrentDomain.RelativeSearchPath ?? AppDomain.CurrentDomain.BaseDirectory);

                #region Add the TrustStore certificate

                // Get the cer file location
                string pfxLocation = executableLocation + "\\Certificates\\TheirCertificate.cer";

                // Add the certificate
                X509Certificate2 theirCert = new X509Certificate2();
                theirCert.Import(pfxLocation, "Password", X509KeyStorageFlags.DefaultKeySet);
                handler.ClientCertificates.Add(theirCert);
                #endregion

                #region Add the KeyStore 
                // Get the location
                pfxLocation = executableLocation + "\\Certificates\\YourCert.pfx";

                // Add the Certificate
                X509Certificate2 YourCert = new X509Certificate2();
                YourCert.Import(pfxLocation, "PASSWORD", X509KeyStorageFlags.DefaultKeySet);
                handler.ClientCertificates.Add(YourCert);
                #endregion

                #endregion

Also – you need to handle cert errors (note: this is BAD – it says ALL cert issues are okay) you should change this code to handle specific cert issues like Name Mismatch. it’s on my list to do. There are plenty of example on how to do this.

This code at the top of your method

// Ignore Certificate errors  need to fix to only handle 
ServicePointManager.ServerCertificateValidationCallback = MyCertHandler;

Method somewhere in your class

private bool MyCertHandler(object sender, X509Certificate certificate, X509Chain chain, SslPolicyErrors error)
    {
        // Ignore errors
        return true;
    }