Basic AccessInfo plugin

Generally we want people to use the existing plugins to manage their
authentication, however there are a number of existing services that
know how to work with an AccessInfo object directly and either cache it
or manipulate it manually.

Provide a simple Identity plugin that just takes an existing AccessInfo
and allows it to be used as an authentication plugin.

Change-Id: I388283c03a0a8a3d1afe43138eebbe5e66ca9102

keystoneclient/auth/identity/access.py

@@ -0,0 +1,47 @@
+# 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.
+
+from keystoneclient.auth.identity import base
+from keystoneclient import utils
+
+
+class AccessInfoPlugin(base.BaseIdentityPlugin):
+    """A plugin that turns an existing AccessInfo object into a usable plugin.
+
+    There are cases where reuse of an auth_ref or AccessInfo object is
+    warranted such as from a cache, from auth_token middleware, or another
+    source.
+
+    Turn the existing access info object into an identity plugin. This plugin
+    cannot be refreshed as the AccessInfo object does not contain any
+    authorizing information.
+
+    :param auth_ref: the existing AccessInfo object.
+    :type auth_ref: keystoneclient.access.AccessInfo
+    :param auth_url: the url where this AccessInfo was retrieved from. Required
+                     if using the AUTH_INTERFACE with get_endpoint. (optional)
+    """
+
+    @utils.positional()
+    def __init__(self, auth_ref, auth_url=None):
+        super(AccessInfoPlugin, self).__init__(auth_url=auth_url,
+                                               reauthenticate=False)
+        self.auth_ref = auth_ref
+
+    def get_auth_ref(self, session, **kwargs):
+        return self.auth_ref
+
+    def invalidate(self):
+        # NOTE(jamielennox): Don't allow the default invalidation to occur
+        # because on next authentication request we will only get the same
+        # auth_ref object again.
+        return False