Sample of SSL-pinning via NSUrlSession for Xamarin.iOS.

ssl-pinning.cs

internal static class Samples
{
    public static void MakeRequest()
    {
        var s = "https://secure-domain.org";
        var request = new NSMutableUrlRequest(new NSUrl(s))
        {
            HttpMethod = "GET"
        };
        
        var session = NSUrlSession.FromConfiguration(NSUrlSessionConfiguration.DefaultSessionConfiguration, 
                                                     (INSUrlSessionDelegate)new MySessionDelegate(),
                                                     new NSOperationQueue());

        NSUrlSessionTask task = session.CreateDataTask(request, (data, response, error) =>
        {
            Debug.WriteLine("data is " + data + " response is " + response + " error is " + error);
        });

        task.Resume();
    }

    public class MySessionDelegate : NSUrlSessionDelegate
    {
        public override void DidReceiveChallenge(NSUrlSession session, NSUrlAuthenticationChallenge challenge, Action<NSUrlSessionAuthChallengeDisposition, NSUrlCredential> completionHandler)
        {
            Debug.WriteLine("challenge is " + challenge.ProtectionSpace.AuthenticationMethod);

            if (challenge.ProtectionSpace.AuthenticationMethod == NSUrlProtectionSpace.AuthenticationMethodServerTrust.ToString())
            {
                var c = NSUrlCredential.FromTrust(challenge.ProtectionSpace.ServerSecTrust);

                challenge.Sender.UseCredential(c, challenge);

                challenge.Sender.ContinueWithoutCredential(challenge);

                completionHandler(NSUrlSessionAuthChallengeDisposition.UseCredential, c);
            }
            else
            {
                var password = "cert-pass";
                var path = Path.Combine(NSBundle.MainBundle.BundlePath, "bundle/path/to/sert.p12");
                var options = NSDictionary.FromObjectAndKey(NSObject.FromObject(password), SecImportExport.Passphrase);
                var certData = File.ReadAllBytes(path);

                SecImportExport.ImportPkcs12(certData, options, out NSDictionary[] importResult);
                var identityHandle = importResult[0][SecImportExport.Identity];
                var identity = new SecIdentity(identityHandle.Handle);
                var cert = new X509Certificate(certData, password);
                var certificate = new SecCertificate(cert.GetRawCertData());
                var cred = NSUrlCredential.FromIdentityCertificatesPersistance(identity, new[] { certificate }, NSUrlCredentialPersistence.ForSession);

                completionHandler(NSUrlSessionAuthChallengeDisposition.UseCredential, cred);
            }
        }
    }
}

More details:

• https://stackoverflow.com/a/22814390/5925490