Add simple Bearer authenticator filter for Kube

* Default file based implementation
* Define some simple interfaces
* Add -token_auth_file to apiserver that will start the apiserver
  with a request filter for tokens

pkg/auth/user/doc.go

@@ -0,0 +1,19 @@
+/*
+Copyright 2014 Google Inc. All rights reserved.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+// Package user contains utilities for dealing with simple user exchange in the auth
+// packages. The user.Info interface defines an interface for exchanging that info.
+package user