.. Copyright 2011-2013 OpenStack Foundation 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 mechanism, 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. This documentation describes the implementation in :class:`keystonemiddleware.auth_token` 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 * if invalid, or no 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 operate in a 'delegated mode'. In this mode, the decision to 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 Oslo 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: .. code-block:: ini [app:myService] paste.app_factory = myService:app_factory [pipeline:main] pipeline = authtoken myService [filter:authtoken] paste.filter_factory = keystonemiddleware.auth_token:filter_factory # Prefix to prepend at the beginning of the path (string # value) #auth_admin_prefix= # Host providing the admin Identity API endpoint (string # value) auth_host=127.0.0.1 # Port of the admin Identity API endpoint (integer value) auth_port=35357 # Protocol of the admin Identity API endpoint(http or https) # (string value) auth_protocol=https # Complete public Identity API endpoint (string value) #auth_uri= # API version of the admin Identity API endpoint (string # value) #auth_version= # Do not handle authorization requests within the middleware, # but delegate the authorization decision to downstream WSGI # components (boolean value) #delay_auth_decision=false # Request timeout value for communicating with Identity API # server. (boolean value) #http_connect_timeout= # How many times are we trying to reconnect when communicating # with Identity API Server. (integer value) #http_request_max_retries=3 # Single shared secret with the Keystone configuration used # for bootstrapping a Keystone installation, or otherwise # bypassing the normal authentication process. (string value) #admin_token= # Keystone account username (string value) #admin_user= # Keystone account password (string value) admin_password=SuperSekretPassword # Keystone service account tenant name to validate user tokens # (string value) #admin_tenant_name=admin # Env key for the swift cache (string value) #cache= # Required if Keystone server requires client certificate # (string value) #certfile= # Required if Keystone server requires client certificate # (string value) #keyfile= # A PEM encoded Certificate Authority to use when verifying # HTTPs connections. Defaults to system CAs. (string value) #cafile= # Verify HTTPS connections. (boolean value) #insecure=false # Directory used to cache files related to PKI tokens (string # value) #signing_dir= # If defined, the memcache server(s) to use for caching (list # value) # Deprecated group/name - [DEFAULT]/memcache_servers #memcached_servers= # In order to prevent excessive requests and validations, the # middleware uses an in-memory cache for the tokens the # Keystone API returns. This is only valid if memcache_servers # is defined. Set to -1 to disable caching completely. # (integer value) #token_cache_time=300 # Value only used for unit testing (integer value) #revocation_cache_time=1 # (optional) if defined, indicate whether token data should be # authenticated or authenticated and encrypted. Acceptable # values are MAC or ENCRYPT. If MAC, token data is # authenticated (with HMAC) in the cache. If ENCRYPT, token # data is encrypted and authenticated in the cache. If the # value is not one of these options or empty, auth_token will # raise an exception on initialization. (string value) #memcache_security_strategy= # (optional, mandatory if memcache_security_strategy is # defined) this string is used for key derivation. (string # value) #memcache_secret_key= # (optional) indicate whether to set the X-Service-Catalog # header. If False, middleware will not ask for service # catalog on token validation and will not set the X-Service- # Catalog header. (boolean value) #include_service_catalog=true # Used to control the use and type of token binding. Can be # set to: "disabled" to not check token binding. "permissive" # (default) to validate binding information if the bind type # is of a form known to the server and ignore it if not. # "strict" like "permissive" but if the bind type is unknown # the token will be rejected. "required" any form of token # binding is needed to be allowed. Finally the name of a # binding method that must be present in tokens. (string # value) #enforce_token_bind=permissive For services which have a separate paste-deploy ini file, auth_token middleware can be alternatively configured in [keystone_authtoken] section in the main config file. For example in Nova, all middleware parameters can be removed from ``api-paste.ini``: .. code-block:: ini [filter:authtoken] paste.filter_factory = keystonemiddleware.auth_token:filter_factory and set in ``nova.conf``: .. code-block:: ini [DEFAULT] auth_strategy=keystone [keystone_authtoken] auth_host = 127.0.0.1 auth_port = 35357 auth_protocol = http admin_user = admin admin_password = SuperSekretPassword admin_tenant_name = service # Any of the options that could be set in api-paste.ini can be set here. Note that middleware parameters in paste config take priority, they must be removed to use values in [keystone_authtoken] section. Configuration Options --------------------- * ``auth_admin_prefix``: Prefix to prepend at the beginning of the path * ``auth_host``: (required) the host providing the keystone service API endpoint for validating and requesting tokens * ``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`) * ``auth_version``: API version of the admin Identity API endpoint * ``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. * ``http_connect_timeout``: (optional) Request timeout value for communicating with Identity API server. * ``http_request_max_retries``: (default 3) How many times are we trying to reconnect when communicating with Identity API Server. * ``http_handler``: (optional) Allows to pass in the name of a fake http_handler callback function used instead of `httplib.HTTPConnection` or `httplib.HTTPSConnection`. Useful for unit testing where network is not available. * ``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. * ``cache``: (optional) Env key for the swift cache * ``certfile``: (required, if Keystone server requires client cert) * ``keyfile``: (required, if Keystone server requires client cert) This can be the same as the certfile if the certfile includes the private key. * ``cafile``: (optional, defaults to use system CA bundle) the path to a PEM encoded CA file/bundle that will be used to verify HTTPS connections. * ``insecure``: (optional, default `False`) Don't verify HTTPS connections (overrides `cafile`). * ``signing_dir``: (optional) Directory used to cache files related to PKI tokens * ``memcached_servers``: (optional) If defined, the memcache server(s) to use for caching * ``token_cache_time``: (default 300) In order to prevent excessive requests and validations, the middleware uses an in-memory cache for the tokens the Keystone API returns. This is only valid if memcache_servers s defined. Set to -1 to disable caching completely. * ``memcache_security_strategy``: (optional) if defined, indicate whether token data should be authenticated or authenticated and encrypted. Acceptable values are MAC or ENCRYPT. If MAC, token data is authenticated (with HMAC) in the cache. If ENCRYPT, token data is encrypted and authenticated in the cache. If the value is not one of these options or empty, auth_token will raise an exception on initialization. * ``memcache_secret_key``: (mandatory if memcache_security_strategy is defined) this string is used for key derivation. * ``include_service_catalog``: (optional, default `True`) Indicate whether to set the X-Service-Catalog header. If False, middleware will not ask for service catalog on token validation and will not set the X-Service-Catalog header. * ``enforce_token_bind``: (default ``permissive``) Used to control the use and type of token binding. Can be set to: "disabled" to not check token binding. "permissive" (default) to validate binding information if the bind type is of a form known to the server and ignore it if not. "strict" like "permissive" but if the bind type is unknown the token will be rejected. "required" any form of token binding is needed to be allowed. Finally the name of a binding method that must be present in tokens. Caching for improved response ----------------------------- In order to prevent excessive requests and validations, the middleware uses an in-memory cache for the tokens the keystone API returns. Keep in mind that invalidated tokens may continue to work if they are still in the token cache, so token_cache_time is configurable. For larger deployments, the middleware also supports memcache based caching. * ``memcached_servers``: (optonal) if defined, the memcache server(s) to use for cacheing. It will be ignored if Swift MemcacheRing is used instead. * ``token_cache_time``: (optional, default 300 seconds) Set to -1 to disable caching completely. When deploying auth_token middleware with Swift, user may elect to use Swift MemcacheRing instead of the local Keystone memcache. The Swift MemcacheRing object is passed in from the request environment and it defaults to 'swift.cache'. However it could be different, depending on deployment. To use Swift MemcacheRing, you must provide the ``cache`` option. * ``cache``: (optional) if defined, the environment key where the Swift MemcacheRing object is stored. Memcached dependencies ====================== In order to use `memcached`_ it is necessary to install the `python-memcached`_ library. If data stored in `memcached`_ will need to be encrypted it is also necessary to install the `pycrypto`_ library. These libs are not listed in the requirements.txt file. .. _`memcached`: http://memcached.org/ .. _`python-memcached`: https://pypi.python.org/pypi/python-memcached .. _`pycrypto`: https://pypi.python.org/pypi/pycrypto Memcached and System Time ========================= When using `memcached`_ with ``auth_token`` middleware, ensure that the system time of memcached hosts is set to UTC. Memcached uses the host's system time in determining whether a key has expired, whereas Keystone sets key expiry in UTC. The timezone used by Keystone and memcached must match if key expiry is to behave as expected. Memcache Protection =================== When using memcached, we are storing user tokens and token validation information into the cache as raw data. Which means that anyone who has access to the memcache servers can read and modify data stored there. To mitigate this risk, ``auth_token`` middleware provides an option to authenticate and optionally encrypt the token data stored in the cache. * ``memcache_security_strategy``: (optional) if defined, indicate whether token data should be authenticated or authenticated and encrypted. Acceptable values are ``MAC`` or ``ENCRYPT``. If ``MAC``, token data is authenticated (with HMAC) in the cache. If ``ENCRYPT``, token data is encrypted and authenticated in the cache. If the value is not one of these options or empty, ``auth_token`` will raise an exception on initialization. * ``memcache_secret_key``: (optional, mandatory if ``memcache_security_strategy`` is defined) this string is used for key derivation. If ``memcache_security_strategy`` is defined and ``memcache_secret_key`` is absent, ``auth_token`` will raise an exception on initialization. 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. An ``X-Service-Token`` header may also be included with a request. If present, and the value of ``X-Auth-Token`` or ``X-Storage-Token`` has not caused the request to be denied, then the middleware will attempt to validate the value of ``X-Service-Token``. If valid, the authentication middleware extends the HTTP request with the header ``X-Service-Identity-Status`` having value `Confirmed` and also extends the request with additional headers representing the identity authenticated and authorised by the token. If ``X-Service-Token`` is present and its value is invalid and the ``delay_auth_decision`` option is True then the value of ``X-Service-Identity-Status`` is set to `Invalid` and no further headers are added. Otherwise if ``X-Service-Token`` is present and its value is invalid then the middleware will respond to the HTTP request with HTTPUnauthorized, regardless of the validity of the ``X-Auth-Token`` or ``X-Storage-Token`` values. Extended the request with additional User Information ----------------------------------------------------- :py:class:`keystonemiddleware.auth_token.AuthProtocol` extends the request with additional information if the user has been authenticated. See the "What we add to the request for use by the OpenStack service" section in :py:mod:`keystonemiddleware.auth_token` for the list of fields set by the auth_token middleware. References ========== .. [PEP-333] pep0333 Phillip J Eby. 'Python Web Server Gateway Interface v1.0.'' http://www.python.org/dev/peps/pep-0333/.