Add client auth plugin framework for kubectl with GCP auth plugin.

pkg/client/restclient/config.go

@@ -30,6 +30,7 @@ import (
 
 	"k8s.io/kubernetes/pkg/api"
 	"k8s.io/kubernetes/pkg/api/unversioned"
+	clientcmdapi "k8s.io/kubernetes/pkg/client/unversioned/clientcmd/api"
 	"k8s.io/kubernetes/pkg/runtime"
 	"k8s.io/kubernetes/pkg/util/crypto"
 	"k8s.io/kubernetes/pkg/version"
@@ -65,6 +66,9 @@ type Config struct {
 	// Impersonate is the username that this RESTClient will impersonate
 	Impersonate string
 
+	// Server requires plugin-specified authentication.
+	AuthProvider *clientcmdapi.AuthProviderConfig
+
 	// TLSClientConfig contains settings to enable transport layer security
 	TLSClientConfig