introduce go client style config creating functions

src/KubernetesClientConfiguration.InCluster.cs

@@ -0,0 +1,35 @@
+using System;
+using System.IO;
+using System.Security.Cryptography.X509Certificates;
+using k8s.Exceptions;
+
+namespace k8s
+{
+    public partial class KubernetesClientConfiguration
+    {
+        private const string ServiceAccountTokenKey = "token";
+        private const string ServiceAccountRootCAKey = "ca.crt";
+
+        public static KubernetesClientConfiguration InClusterConfig()
+        {
+            var host = Environment.GetEnvironmentVariable("KUBERNETES_SERVICE_HOST");
+            var port = Environment.GetEnvironmentVariable("KUBERNETES_SERVICE_PORT");
+
+            if (string.IsNullOrWhiteSpace(host) || string.IsNullOrWhiteSpace(port))
+            {
+                throw new KubeConfigException(
+                    "unable to load in-cluster configuration, KUBERNETES_SERVICE_HOST and KUBERNETES_SERVICE_PORT must be defined");
+            }
+
+            var token = File.ReadAllText("/var/run/secrets/kubernetes.io/serviceaccount/" + ServiceAccountTokenKey);
+            var rootCAFile = "/var/run/secrets/kubernetes.io/serviceaccount/" + ServiceAccountRootCAKey;
+
+            return new KubernetesClientConfiguration
+            {
+                Host = new UriBuilder("https", host, Convert.ToInt32(port)).ToString(),
+                AccessToken = token,
+                SslCaCert = Utils.LoadPemFileCert(rootCAFile)
+            };
+        }
+    }
+}