python-keystoneclient/doc/source/middlewarearchitecture.rst

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 architecture. This documentation primarily describes the implementation in keystoneclient/middleware/auth_token.py (:pykeystoneclient.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.

Authentication Component

Figure 1. 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 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.

Authentication Component (Delegated Mode)

Figure 2. Authentication Component (Delegated Mode)

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 = authtoken myService

[filter:authtoken]
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 to use Swift MemcacheRing
;cache = swift.cache
;Uncomment next line and check ip:port to use memcached to cache tokens
;memcached_servers = 127.0.0.1:11211
;Uncomment next 2 lines to turn on memcache protection
;memcache_security_strategy = ENCRYPT
;memcache_secret_key = change_me
;Uncomment next 2 lines if Keystone server is validating client cert
;certfile = <path to middleware public cert>
;keyfile = <path to middleware private cert>
;Uncomment next line to opt-out of service catalog
;include_service_catalog = False

For services which have 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 = keystone.middleware.auth_token:filter_factory

and set in nova.conf:

[DEFAULT]
...
auth_strategy=keystone

[keystone_authtoken]
auth_host = 127.0.0.1
auth_port = 35357
auth_protocol = http
auth_uri = http://127.0.0.1:5000/
admin_user = admin
admin_password = SuperSekretPassword
admin_tenant_name = service

Note that middleware parameters in paste config take priority, they must be removed to use values in [keystone_authtoken] section.

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.
• http_connect_timeout: (optional, default python default allow increase the timeout when validating token by http).
• 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)
• 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).
• 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.

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 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.

Extended the request with additional User Information

:pykeystone.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/.