Fix issue with X509VerificationFlags.AllowUnknownCertificateAuthority behavior (#174)

* Fix issue with X509VerificationFlags.AllowUnknownCertificateAuthority behavior

* Add CertificateValidationTests

tests/KubernetesClient.Tests/CertificateValidationTests.cs

@@ -0,0 +1,37 @@
+using System;
+using System.IO;
+using System.Net.Security;
+using System.Security.Cryptography.X509Certificates;
+using Xunit;
+
+namespace k8s.tests
+{
+    public class CertificateValidationTests
+    {
+        [Fact]
+        public void ValidCert()
+        {
+            var caCert = new X509Certificate2("assets/ca.crt");
+            var testCert = new X509Certificate2("assets/ca.crt");
+            var chain = new X509Chain();
+            var errors = SslPolicyErrors.RemoteCertificateChainErrors;
+
+            var result = Kubernetes.CertificateValidationCallBack(this, caCert, testCert, chain, errors);
+
+            Assert.True(result);
+        }
+
+        [Fact]
+        public void InvalidCert()
+        {
+            var caCert = new X509Certificate2("assets/ca.crt");
+            var testCert = new X509Certificate2("assets/ca2.crt");
+            var chain = new X509Chain();
+            var errors = SslPolicyErrors.RemoteCertificateChainErrors;
+
+            var result = Kubernetes.CertificateValidationCallBack(this, caCert, testCert, chain, errors);
+
+            Assert.False(result);
+        }
+    }
+}