NSUrlSessionDataDelegate.cs

        class DataTaskDelegate : NSUrlSessionDataDelegate
        {
            NSUrlSessionHandler This { get; set; }

            public DataTaskDelegate(NSUrlSessionHandler that)
            {
                this.This = that;
            }

            public override void DidReceiveChallenge(NSUrlSession session, NSUrlSessionTask task, NSUrlAuthenticationChallenge challenge, Action<NSUrlSessionAuthChallengeDisposition, NSUrlCredential> completionHandler)
            {
                if (This.certVerification == CertificateVerification.Normal ||
                        challenge.ProtectionSpace == null ||
                        challenge.ProtectionSpace.AuthenticationMethod != "NSURLAuthenticationMethodServerTrust") {

                    // XXX: This throws ArgumentNullException, but according to Apple 
                    // Docs, this is how you indicate you want default result: "For 
                    // other challenges, the ones that you don't care about, call the 
                    // completion handler block with the 
                    // NSURLSessionAuthChallengePerformDefaultHandling disposition and 
                    // a NULL credential."
                    // https://developer.apple.com/library/ios/technotes/tn2232/_index.html#//apple_ref/doc/uid/DTS40012884-CH1-SECNSURLSESSION
                    completionHandler(NSUrlSessionAuthChallengeDisposition.PerformDefaultHandling, null);
                }

                Console.WriteLine("Performing INSECURE request to {0}", task.CurrentRequest.Url.AbsoluteString);
                completionHandler(NSUrlSessionAuthChallengeDisposition.UseCredential, NSUrlCredential.FromTrust(new SecTrust(IntPtr.Zero)));
            }
        }