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Copyright 2011-2013 OpenStack Foundation
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All Rights Reserved.
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Licensed under the Apache License, Version 2.0 (the "License"); you may
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not use this file except in compliance with the License. You may obtain
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a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
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WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
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License for the specific language governing permissions and limitations
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under the License.
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=======================
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Middleware Architecture
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=======================
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Abstract
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========
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The Keystone middleware architecture supports a common authentication protocol
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in use between the OpenStack projects. By using keystone as a common
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authentication and authorization mechanism, the OpenStack project can plug in
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to existing authentication and authorization systems in use by existing
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environments.
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In this document, we describe the architecture and responsibilities of the
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authentication middleware which acts as the internal API mechanism for
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OpenStack projects based on the WSGI standard.
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This documentation describes the implementation in
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:class:`keystonemiddleware.auth_token`
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Specification Overview
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======================
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'Authentication' is the process of determining that users are who they say they
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are. Typically, 'authentication protocols' such as HTTP Basic Auth, Digest
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Access, public key, token, etc, are used to verify a user's identity. In this
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document, we define an ''authentication component'' as a software module that
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implements an authentication protocol for an OpenStack service. OpenStack is
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using a token based mechanism to represent authentication and authorization.
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At a high level, an authentication middleware component is a proxy that
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intercepts HTTP calls from clients and populates HTTP headers in the request
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context for other WSGI middleware or applications to use. The general flow
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of the middleware processing is:
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* clear any existing authorization headers to prevent forgery
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* collect the token from the existing HTTP request headers
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* validate the token
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* if valid, populate additional headers representing the identity that has
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been authenticated and authorized
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* if invalid, or no token present, reject the request (HTTPUnauthorized)
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or pass along a header indicating the request is unauthorized (configurable
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in the middleware)
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* if the keystone service is unavailable to validate the token, reject
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the request with HTTPServiceUnavailable.
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.. _authComponent:
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Authentication Component
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------------------------
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Figure 1. Authentication Component
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.. image:: images/graphs_authComp.svg
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:width: 100%
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:height: 180
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:alt: An Authentication Component
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The middleware may also be configured to operate in a 'delegated mode'.
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In this mode, the decision to reject an unauthenticated client is delegated to
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the OpenStack service, as illustrated in :ref:`authComponentDelegated`.
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Here, requests are forwarded to the OpenStack service with an identity status
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message that indicates whether the client's identity has been confirmed or is
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indeterminate. It is the OpenStack service that decides whether or not a reject
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message should be sent to the client.
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.. _authComponentDelegated:
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Authentication Component (Delegated Mode)
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-----------------------------------------
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Figure 2. Authentication Component (Delegated Mode)
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.. image:: images/graphs_authCompDelegate.svg
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:width: 100%
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:height: 180
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:alt: An Authentication Component (Delegated Mode)
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.. _deployStrategies:
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Deployment Strategy
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===================
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The middleware is intended to be used inline with OpenStack wsgi components,
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based on the Oslo WSGI middleware class. It is typically deployed
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as a configuration element in a paste configuration pipeline of other
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middleware components, with the pipeline terminating in the service
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application. The middleware conforms to the python WSGI standard [PEP-333]_.
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In initializing the middleware, a configuration item (which acts like a python
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dictionary) is passed to the middleware with relevant configuration options.
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Configuration
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-------------
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The middleware is configured within the config file of the main application as
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a WSGI component. Example for the auth_token middleware:
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.. code-block:: ini
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[app:myService]
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paste.app_factory = myService:app_factory
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[pipeline:main]
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pipeline = authtoken myService
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[filter:authtoken]
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paste.filter_factory = keystonemiddleware.auth_token:filter_factory
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.. literalinclude:: _static/keystonemiddleware.conf.sample
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If the ``auth_plugin`` configuration option is set, you may need to refer to
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the `Authentication Plugins <http://docs.openstack.org/developer/
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python-keystoneclient/authentication-plugins.html>`_ document for how to
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configure the auth_token middleware.
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For services which have a separate paste-deploy ini file, auth_token middleware
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can be alternatively configured in [keystone_authtoken] section in the main
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config file. For example in Nova, all middleware parameters can be removed
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from ``api-paste.ini``:
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.. code-block:: ini
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[filter:authtoken]
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paste.filter_factory = keystonemiddleware.auth_token:filter_factory
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and set in ``nova.conf``:
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.. code-block:: ini
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[DEFAULT]
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auth_strategy=keystone
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[keystone_authtoken]
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auth_host = 127.0.0.1
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auth_port = 35357
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auth_protocol = http
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admin_user = admin
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admin_password = SuperSekretPassword
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admin_tenant_name = service
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# Any of the options that could be set in api-paste.ini can be set here.
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.. NOTE::
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Middleware parameters in paste config take priority and must be removed
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to use options in the [keystone_authtoken] section.
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The following is an example of a service's auth_token middleware configuration
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when ``auth_plugin`` is set to ``password``.
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.. code-block:: ini
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[keystone_authtoken]
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auth_plugin = password
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project_domain_name = Default
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project_name = service
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user_domain_name = Default
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username = nova
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password = ServicePassword
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auth_url = http://127.0.0.1:35357
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# Any of the options that could be set in api-paste.ini can be set here.
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If the service doesn't use the global oslo.config object (CONF), then the
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olso config project name can be set it in paste config and
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keystonemiddleware will load the project configuration itself.
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Optionally the location of the configuration file can be set if oslo.config
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is not able to discover it.
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.. code-block:: ini
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[filter:authtoken]
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paste.filter_factory = keystonemiddleware.auth_token:filter_factory
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oslo_config_project = nova
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# oslo_config_file = /not_discoverable_location/nova.conf
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Configuration Options
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---------------------
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* ``auth_plugin``: This is the plugin used for authentication, such as
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password and token. For example, if the ``auth_plugin`` configuration option
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is set to ``password`` then set ``username``, ``password``, ``project_name``,
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``project_domain_name``, ``user_domain_name`` and ``auth_url`` accordingly.
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* ``auth_admin_prefix``: Prefix to prepend at the beginning of the path
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* ``auth_host``: (required) the host providing the keystone service API endpoint
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for validating and requesting tokens
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* ``auth_port``: (optional, default `35357`) the port used to validate tokens
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* ``auth_protocol``: (optional, default `https`)
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* ``auth_uri``: (optional, defaults to
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`auth_protocol`://`auth_host`:`auth_port`)
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* ``auth_version``: API version of the admin Identity API endpoint
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* ``delay_auth_decision``: (optional, default `0`) (off). If on, the middleware
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will not reject invalid auth requests, but will delegate that decision to
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downstream WSGI components.
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* ``http_connect_timeout``: (optional) Request timeout value for communicating
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with Identity API server.
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* ``http_request_max_retries``: (default 3) How many times are we trying to
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reconnect when communicating with Identity API Server.
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* ``http_handler``: (optional) Allows to pass in the name of a fake
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http_handler callback function used instead of `httplib.HTTPConnection` or
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`httplib.HTTPSConnection`. Useful for unit testing where network is not
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available.
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* ``admin_token``: either this or the following three options are required. If
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set, this is a single shared secret with the keystone configuration used to
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validate tokens.
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* ``admin_user``, ``admin_password``, ``admin_tenant_name``: if ``admin_token``
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is not set, or invalid, then admin_user, admin_password, and
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admin_tenant_name are defined as a service account which is expected to have
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been previously configured in Keystone to validate user tokens.
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* ``cache``: (optional) Env key for the swift cache
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* ``certfile``: (required, if Keystone server requires client cert)
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* ``keyfile``: (required, if Keystone server requires client cert) This can be
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the same as the certfile if the certfile includes the private key.
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* ``cafile``: (optional, defaults to use system CA bundle) the path to a PEM
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encoded CA file/bundle that will be used to verify HTTPS connections.
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* ``insecure``: (optional, default `False`) Don't verify HTTPS connections
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(overrides `cafile`).
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* ``signing_dir``: (optional) Directory used to cache files related to PKI
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tokens
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* ``memcached_servers``: (optional) If defined, the memcached server(s) to use
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for caching
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* ``token_cache_time``: (default 300) In order to prevent excessive requests
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and validations, the middleware uses an in-memory cache for the tokens the
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Keystone API returns. This is only valid if memcache_servers s defined. Set
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to -1 to disable caching completely.
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* ``memcache_security_strategy``: (optional) if defined, indicate whether token
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data should be authenticated or authenticated and encrypted. Acceptable
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values are MAC or ENCRYPT. If MAC, token data is authenticated (with HMAC)
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in the cache. If ENCRYPT, token data is encrypted and authenticated in the
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cache. If the value is not one of these options or empty, auth_token will
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raise an exception on initialization.
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* ``memcache_secret_key``: (mandatory if memcache_security_strategy is defined)
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this string is used for key derivation.
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* ``include_service_catalog``: (optional, default `True`) Indicate whether to
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set the X-Service-Catalog header. If False, middleware will not ask for
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service catalog on token validation and will not set the X-Service-Catalog
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header.
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* ``enforce_token_bind``: (default ``permissive``) Used to control the use and
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type of token binding. Can be set to: "disabled" to not check token binding.
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"permissive" (default) to validate binding information if the bind type is of
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a form known to the server and ignore it if not. "strict" like "permissive"
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but if the bind type is unknown the token will be rejected. "required" any
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form of token binding is needed to be allowed. Finally the name of a binding
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method that must be present in tokens.
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Caching for improved response
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-----------------------------
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In order to prevent excessive requests and validations, the middleware uses an
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in-memory cache for the tokens the keystone API returns. Keep in mind that
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invalidated tokens may continue to work if they are still in the token cache,
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so token_cache_time is configurable. For larger deployments, the middleware
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also supports memcache based caching.
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* ``memcached_servers``: (optional) if defined, the memcached server(s) to use for
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caching. It will be ignored if Swift MemcacheRing is used instead.
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* ``token_cache_time``: (optional, default 300 seconds) Set to -1 to disable
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caching completely.
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When deploying auth_token middleware with Swift, user may elect
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to use Swift MemcacheRing instead of the local Keystone memcache.
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The Swift MemcacheRing object is passed in from the request environment
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and it defaults to 'swift.cache'. However it could be
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different, depending on deployment. To use Swift MemcacheRing, you must
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provide the ``cache`` option.
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* ``cache``: (optional) if defined, the environment key where the Swift
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MemcacheRing object is stored.
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Memcached dependencies
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======================
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In order to use `memcached`_ it is necessary to install the `python-memcached`_
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library. If data stored in `memcached`_ will need to be encrypted it is also
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necessary to install the `pycrypto`_ library. These libs are not listed in
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the requirements.txt file.
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.. _`memcached`: http://memcached.org/
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.. _`python-memcached`: https://pypi.python.org/pypi/python-memcached
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.. _`pycrypto`: https://pypi.python.org/pypi/pycrypto
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Memcached and System Time
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=========================
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When using `memcached`_ with ``auth_token`` middleware, ensure that the system
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time of memcached hosts is set to UTC. Memcached uses the host's system
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time in determining whether a key has expired, whereas Keystone sets
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key expiry in UTC. The timezone used by Keystone and memcached must
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match if key expiry is to behave as expected.
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Memcache Protection
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===================
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When using memcached, we are storing user tokens and token validation
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information into the cache as raw data. Which means that anyone who
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has access to the memcached servers can read and modify data stored
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there. To mitigate this risk, ``auth_token`` middleware provides an
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option to authenticate and optionally encrypt the token data stored in
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the cache.
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* ``memcache_security_strategy``: (optional) if defined, indicate
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whether token data should be authenticated or authenticated and
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encrypted. Acceptable values are ``MAC`` or ``ENCRYPT``. If ``MAC``,
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token data is authenticated (with HMAC) in the cache. If
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``ENCRYPT``, token data is encrypted and authenticated in the
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cache. If the value is not one of these options or empty,
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``auth_token`` will raise an exception on initialization.
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* ``memcache_secret_key``: (optional, mandatory if
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``memcache_security_strategy`` is defined) this string is used for
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key derivation. If ``memcache_security_strategy`` is defined and
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``memcache_secret_key`` is absent, ``auth_token`` will raise an
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exception on initialization.
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Exchanging User Information
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===========================
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The middleware expects to find a token representing the user with the header
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``X-Auth-Token`` or ``X-Storage-Token``. `X-Storage-Token` is supported for
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swift/cloud files and for legacy Rackspace use. If the token isn't present and
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the middleware is configured to not delegate auth responsibility, it will
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respond to the HTTP request with HTTPUnauthorized, returning the header
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``WWW-Authenticate`` with the value `Keystone uri='...'` to indicate where to
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request a token. The auth_uri returned is configured with the middleware.
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The authentication middleware extends the HTTP request with the header
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``X-Identity-Status``. If a request is successfully authenticated, the value
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is set to `Confirmed`. If the middleware is delegating the auth decision to the
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service, then the status is set to `Invalid` if the auth request was
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unsuccessful.
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An ``X-Service-Token`` header may also be included with a request. If present,
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and the value of ``X-Auth-Token`` or ``X-Storage-Token`` has not caused the
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request to be denied, then the middleware will attempt to validate the value of
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``X-Service-Token``. If valid, the authentication middleware extends the HTTP
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request with the header ``X-Service-Identity-Status`` having value `Confirmed`
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and also extends the request with additional headers representing the identity
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authenticated and authorised by the token.
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If ``X-Service-Token`` is present and its value is invalid and the
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``delay_auth_decision`` option is True then the value of
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``X-Service-Identity-Status`` is set to `Invalid` and no further headers are
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added. Otherwise if ``X-Service-Token`` is present and its value is invalid
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then the middleware will respond to the HTTP request with HTTPUnauthorized,
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regardless of the validity of the ``X-Auth-Token`` or ``X-Storage-Token``
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values.
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Extended the request with additional User Information
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-----------------------------------------------------
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:py:class:`keystonemiddleware.auth_token.AuthProtocol` extends the
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request with additional information if the user has been authenticated. See the
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"What we add to the request for use by the OpenStack service" section in
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:py:mod:`keystonemiddleware.auth_token` for the list of fields set by
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the auth_token middleware.
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References
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==========
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.. [PEP-333] pep0333 Phillip J Eby. 'Python Web Server Gateway Interface
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v1.0.'' http://www.python.org/dev/peps/pep-0333/.
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