webhook: use rest.Config instead of kubeconfig file as input

This change updates the generic webhook logic to use a rest.Config
as its input instead of a kubeconfig file.  This exposes all of the
rest.Config knobs to the caller instead of the more limited set
available through the kubeconfig format.  This is useful when this
code is being used as a library outside of core Kubernetes. For
example, a downstream consumer may want to override the webhook's
internals such as its TLS configuration.

Signed-off-by: Monis Khan <mok@vmware.com>

test/integration/auth/auth_test.go

@@ -57,6 +57,7 @@ import (
 	"k8s.io/apiserver/pkg/authentication/user"
 	"k8s.io/apiserver/pkg/authorization/authorizer"
 	"k8s.io/apiserver/pkg/authorization/authorizerfactory"
+	webhookutil "k8s.io/apiserver/pkg/util/webhook"
 	"k8s.io/apiserver/plugin/pkg/authenticator/token/tokentest"
 	"k8s.io/apiserver/plugin/pkg/authenticator/token/webhook"
 	clientset "k8s.io/client-go/kubernetes"
@@ -109,7 +110,13 @@ func getTestWebhookTokenAuth(serverURL string, customDial utilnet.DialFunc) (aut
 		Jitter:   0.2,
 		Steps:    5,
 	}
-	webhookTokenAuth, err := webhook.New(kubecfgFile.Name(), "v1beta1", nil, retryBackoff, customDial)
+
+	clientConfig, err := webhookutil.LoadKubeconfig(kubecfgFile.Name(), customDial)
+	if err != nil {
+		return nil, err
+	}
+
+	webhookTokenAuth, err := webhook.New(clientConfig, "v1beta1", nil, retryBackoff)
 	if err != nil {
 		return nil, err
 	}