..
      Copyright 2011-2012 OpenStack, LLC
      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.

=======================
Middleware Architecture
=======================

Abstract
========

The Keystone middleware architecture supports a common authentication protocol
in use between the OpenStack projects. By using keystone as a common
authentication and authorization mechanisms, the OpenStack project can plug in
to existing authentication and authorization systems in use by existing
environments.

In this document, we describe the architecture and responsibilities of the
authentication middleware which acts as the internal API mechanism for
OpenStack projects based on the WSGI standard.

For the architecture of keystone and its services, please see
:doc:`architecture`. This documentation primarily describes the implementation
in ``keystone/middleware/auth_token.py``
(:py:class:`keystone.middleware.auth_token.AuthProtocol`)

Specification Overview
======================

'Authentication' is the process of determining that users are who they say they
are. Typically, 'authentication protocols' such as HTTP Basic Auth, Digest
Access, public key, token, etc, are used to verify a user's identity. In this
document, we define an ''authentication component'' as a software module that
implements an authentication protocol for an OpenStack service. OpenStack is
using a token based mechanism to represent authentication and authorization.

At a high level, an authentication middleware component is a proxy that
intercepts HTTP calls from clients and populates HTTP headers in the request
context for other WSGI middleware or applications to use. The general flow
of the middleware processing is:

* clear any existing authorization headers to prevent forgery
* collect the token from the existing HTTP request headers
* validate the token

  * if valid, populate additional headers representing the identity that has
    been authenticated and authorized
  * in invalid, or not token present, reject the request (HTTPUnauthorized)
    or pass along a header indicating the request is unauthorized (configurable
    in the middleware)
  * if the keystone service is unavailable to validate the token, reject
    the request with HTTPServiceUnavailable.

.. _authComponent:

Authentication Component
------------------------

Figure 1. Authentication Component

.. image:: images/graphs_authComp.svg
   :width: 100%
   :height: 180
   :alt: An Authentication Component

The middleware may also be configured to operated in a 'delegated mode'.
In this mode, the decision reject an unauthenticated client is delegated to
the OpenStack service, as illustrated in :ref:`authComponentDelegated`.

Here, requests are forwarded to the OpenStack service with an identity status
message that indicates whether the client's identity has been confirmed or is
indeterminate. It is the OpenStack service that decides whether or not a reject
message should be sent to the client.

.. _authComponentDelegated:

Authentication Component (Delegated Mode)
-----------------------------------------

Figure 2. Authentication Component (Delegated Mode)

.. image:: images/graphs_authCompDelegate.svg
   :width: 100%
   :height: 180
   :alt: An Authentication Component (Delegated Mode)

.. _deployStrategies:

Deployment Strategy
===================

The middleware is intended to be used inline with OpenStack wsgi components,
based on the openstack-common WSGI middleware class. It is typically deployed
as a configuration element in a paste configuration pipeline of other
middleware components, with the pipeline terminating in the service
application. The middleware conforms to the python WSGI standard [PEP-333]_.
In initializing the middleware, a configuration item (which acts like a python
dictionary) is passed to the middleware with relevant configuration options.

Configuration
-------------

The middleware is configured within the config file of the main application as
a WSGI component. Example for the auth_token middleware::

    [app:myService]
    paste.app_factory = myService:app_factory

    [pipeline:main]
    pipeline = tokenauth myService

    [filter:tokenauth]
    paste.filter_factory = keystone.middleware.auth_token:filter_factory
    auth_host = 127.0.0.1
    auth_port = 35357
    auth_protocol = http
    auth_uri = http://127.0.0.1:5000/
    admin_token = Super999Sekret888Password777
    admin_user = admin
    admin_password = SuperSekretPassword
    admin_tenant_name = service
    ;Uncomment next line and check ip:port to use memcached to cache tokens
    ;memcache_servers = 127.0.0.1:11211

Configuration Options
---------------------

* ``auth_host``: (required) the host providing the keystone service API endpoint
  for validating and requesting tokens
* ``admin_token``: either this or the following three options are required. If
  set, this is a single shared secret with the keystone configuration used to
  validate tokens.
* ``admin_user``, ``admin_password``, ``admin_tenant_name``: if ``admin_token``
  is not set, or invalid, then admin_user, admin_password, and
  admin_tenant_name are defined as a service account which is expected to have
  been previously configured in Keystone to validate user tokens.

* ``delay_auth_decision``: (optional, default `0`) (off). If on, the middleware
  will not reject invalid auth requests, but will delegate that decision to
  downstream WSGI components.
* ``auth_port``: (optional, default `35357`) the port used to validate tokens
* ``auth_protocol``: (optional, default `https`)
* ``auth_uri``: (optional, defaults to `auth_protocol`://`auth_host`:`auth_port`)

Caching for improved response
-----------------------------

In order to prevent every service request, the middleware may be configured
to utilize a cache, and the keystone API returns the tokens with an
expiration (configurable in duration on the keystone service). The middleware
supports memcache based caching.

* ``memcache_servers``: (optonal) if defined, the memcache server(s) to use for
  cacheing
* ``token_cache_time``: (optional, default 300 seconds) Only valid if
  memcache_servers is defined.

Exchanging User Information
===========================

The middleware expects to find a token representing the user with the header
``X-Auth-Token`` or ``X-Storage-Token``. `X-Storage-Token` is supported for
swift/cloud files and for legacy Rackspace use. If the token isn't present and
the middleware is configured to not delegate auth responsibility, it will
respond to the HTTP request with HTTPUnauthorized, returning the header
``WWW-Authenticate`` with the value `Keystone uri='...'` to indicate where to
request a token. The auth_uri returned is configured  with the middleware.

The authentication middleware extends the HTTP request with the header
``X-Identity-Status``.  If a request is successfully authenticated, the value
is set to `Confirmed`. If the middleware is delegating the auth decision to the
service, then the status is set to `Invalid` if the auth request was
unsuccessful.

Extended the request with additional User Information
-----------------------------------------------------

:py:class:`keystone.middleware.auth_token.AuthProtocol` extends the request
with additional information if the user has been authenticated.


X-Identity-Status
    Provides information on whether the request was authenticated or not.

X-Tenant-Id
    The unique, immutable tenant Id

X-Tenant-Name
    The unique, but mutable (it can change) tenant name.

X-User-Id
    The user id of the user used to log in

X-User-Name
    The username used to log in

X-Roles
    The roles associated with that user

Deprecated additions
--------------------

X-Tenant
    Provides the tenant name. This is to support any legacy implementations
    before Keystone switched to an ID/Name schema for tenants.

X-User
    The username used to log in. This is to support any legacy implementations
    before Keystone switched to an ID/Name schema for tenants.

X-Role
    The roles associated with that user

References
==========

.. [PEP-333] pep0333 Phillip J Eby.  'Python Web Server Gateway Interface
    v1.0.''  http://www.python.org/dev/peps/pep-0333/.
