The keystonemiddleware architecture supports a common authentication protocol in use between the OpenStack projects. By using keystone as a common authentication and authorization mechanism, various OpenStack projects can leverage the existing authentication and authorization systems in use.
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
keystonemiddleware.auth_token
‘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. Bearer tokens are currently the most common authentication protocol used within OpenStack.
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:
The following shows the default behavior of an Authentication Component deployed in front of an OpenStack service.
The Authentication Component, or middleware, will reject any unauthenticated requests, only allowing authenticated requests through to the OpenStack service.
The Authentication Component may be configured to operate in a ‘delegated mode’. In this mode, the decision to reject or accept an unauthenticated client is delegated to the OpenStack service.
Here, requests are forwarded to the OpenStack service with an identity status message that indicates whether the identity of the client has been confirmed or is indeterminate. The consuming OpenStack service decides whether or not a rejection message should be sent to the client.
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.
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 = authtoken myService
[filter:authtoken]
paste.filter_factory = keystonemiddleware.auth_token:filter_factory
[DEFAULT]
If the auth_plugin
configuration option is set, you may need to refer to
the Authentication Plugins document for how to configure the auth_token
middleware.
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
:
[filter:authtoken]
paste.filter_factory = keystonemiddleware.auth_token:filter_factory
and set in nova.conf
:
[DEFAULT]
auth_strategy=keystone
[keystone_authtoken]
identity_uri = http://127.0.0.1:35357
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
Middleware parameters in paste config take priority and must be removed to use options in the [keystone_authtoken] section.
The following is an example of a service’s auth_token middleware configuration
when auth_plugin
is set to password
.
[keystone_authtoken]
auth_plugin = password
project_domain_name = Default
project_name = service
user_domain_name = Default
username = nova
password = ServicePassword
auth_url = http://127.0.0.1:35357
# Any of the options that could be set in api-paste.ini can be set here.
If the service doesn’t use the global oslo.config object (CONF), then the oslo config project name can be set it in paste config and keystonemiddleware will load the project configuration itself. Optionally the location of the configuration file can be set if oslo.config is not able to discover it.
[filter:authtoken]
paste.filter_factory = keystonemiddleware.auth_token:filter_factory
oslo_config_project = nova
# oslo_config_file = /not_discoverable_location/nova.conf
Validating the identity of every client on every request can impact performance for both the OpenStack service and the identity service. As a result, keystonemiddleware is configurable to cache authentication responses from the identity service in-memory. It is worth noting that tokens invalidated after they’ve been stored in the cache may continue to work. Deployments using memcached may use the following keystonemiddleware configuration options instead of an in-memory cache.
memcached_servers
: (optional) if defined, the memcached server(s) to use
for caching. 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.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.
When using memcached, tokens and authentication responses are stored in the
cache as raw data. In the event the cache is compromised, all token and
authentication responses will be readable. 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.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 URI returned is configured with the
www_authenticate_uri
option.
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.
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
keystonemiddleware.auth_token
for the list of fields set by
the auth_token middleware.
[PEP-333] | pep0333 Phillip J Eby. ‘Python Web Server Gateway Interface v1.0.’’ http://www.python.org/dev/peps/pep-0333/. |
Except where otherwise noted, this document is licensed under Creative Commons Attribution 3.0 License. See all OpenStack Legal Documents.