The Auth System

TempAuth

The auth system for Swift is loosely based on the auth system from the existing Rackspace architecture – actually from a few existing auth systems – and is therefore a bit disjointed. The distilled points about it are:

  • The authentication/authorization part can be an external system or a subsystem run within Swift as WSGI middleware
  • The user of Swift passes in an auth token with each request
  • Swift validates each token with the external auth system or auth subsystem and caches the result
  • The token does not change from request to request, but does expire

The token can be passed into Swift using the X-Auth-Token or the X-Storage-Token header. Both have the same format: just a simple string representing the token. Some auth systems use UUID tokens, some an MD5 hash of something unique, some use “something else” but the salient point is that the token is a string which can be sent as-is back to the auth system for validation.

Swift will make calls to the auth system, giving the auth token to be validated. For a valid token, the auth system responds with an overall expiration in seconds from now. Swift will cache the token up to the expiration time.

The included TempAuth also has the concept of admin and non-admin users within an account. Admin users can do anything within the account. Non-admin users can only perform operations per container based on the container’s X-Container-Read and X-Container-Write ACLs. Container ACLs use the “V1” ACL syntax, which looks like this: name1, name2, .r:referrer1.com, .r:-bad.referrer1.com, .rlistings For more information on ACLs, see swift.common.middleware.acl.

Additionally, if the auth system sets the request environ’s swift_owner key to True, the proxy will return additional header information in some requests, such as the X-Container-Sync-Key for a container GET or HEAD.

In addition to container ACLs, TempAuth allows account-level ACLs. Any auth system may use the special header X-Account-Access-Control to specify account-level ACLs in a format specific to that auth system. (Following the TempAuth format is strongly recommended.) These headers are visible and settable only by account owners (those for whom swift_owner is true). Behavior of account ACLs is auth-system-dependent. In the case of TempAuth, if an authenticated user has membership in a group which is listed in the ACL, then the user is allowed the access level of that ACL.

Account ACLs use the “V2” ACL syntax, which is a JSON dictionary with keys named “admin”, “read-write”, and “read-only”. (Note the case sensitivity.) An example value for the X-Account-Access-Control header looks like this: {"admin":["a","b"],"read-only":["c"]} Keys may be absent (as shown). The recommended way to generate ACL strings is as follows:

from swift.common.middleware.acl import format_acl
acl_data = { 'admin': ['alice'], 'read-write': ['bob', 'carol'] }
acl_string = format_acl(version=2, acl_dict=acl_data)

Using the format_acl() method will ensure that JSON is encoded as ASCII (using e.g. ‘u1234’ for Unicode). While it’s permissible to manually send curl commands containing X-Account-Access-Control headers, you should exercise caution when doing so, due to the potential for human error.

Within the JSON dictionary stored in X-Account-Access-Control, the keys have the following meanings:

Access Level Description
read-only These identities can read everything (except privileged headers) in the account. Specifically, a user with read-only account access can get a list of containers in the account, list the contents of any container, retrieve any object, and see the (non-privileged) headers of the account, any container, or any object.
read-write These identities can read or write (or create) any container. A user with read-write account access can create new containers, set any unprivileged container headers, overwrite objects, delete containers, etc. A read-write user can NOT set account headers (or perform any PUT/POST/DELETE requests on the account).
admin These identities have “swift_owner” privileges. A user with admin account access can do anything the account owner can, including setting account headers and any privileged headers – and thus granting read-only, read-write, or admin access to other users.

For more details, see swift.common.middleware.tempauth. For details on the ACL format, see swift.common.middleware.acl.

Users with the special group .reseller_admin can operate on any account. For an example usage please see swift.common.middleware.tempauth. If a request is coming from a reseller the auth system sets the request environ reseller_request to True. This can be used by other middlewares.

TempAuth will now allow OPTIONS requests to go through without a token.

The user starts a session by sending a ReST request to the auth system to receive the auth token and a URL to the Swift system.

Keystone Auth

Swift is able to authenticate against OpenStack keystone via the swift.common.middleware.keystoneauth middleware.

In order to use the keystoneauth middleware the authtoken middleware from keystonemiddleware will need to be configured.

The authtoken middleware performs the authentication token validation and retrieves actual user authentication information. It can be found in the keystonemiddleware distribution.

The keystoneauth middleware performs authorization and mapping the keystone roles to Swift’s ACLs.

Configuring Swift to use Keystone

Configuring Swift to use Keystone is relatively straight forward. The first step is to ensure that you have the auth_token middleware installed, distributed with keystone it can either be dropped in your python path or installed via the keystone package.

You need at first make sure you have a service endpoint of type object-store in keystone pointing to your Swift proxy. For example having this in your /etc/keystone/default_catalog.templates

catalog.RegionOne.object_store.name = Swift Service
catalog.RegionOne.object_store.publicURL = http://swiftproxy:8080/v1/AUTH_$(tenant_id)s
catalog.RegionOne.object_store.adminURL = http://swiftproxy:8080/
catalog.RegionOne.object_store.internalURL = http://swiftproxy:8080/v1/AUTH_$(tenant_id)s

On your Swift Proxy server you will want to adjust your main pipeline and add auth_token and keystoneauth in your /etc/swift/proxy-server.conf like this

[pipeline:main]
pipeline = [....] authtoken keystoneauth proxy-logging proxy-server

add the configuration for the authtoken middleware:

[filter:authtoken]
paste.filter_factory = keystonemiddleware.auth_token:filter_factory
auth_host = keystonehost
auth_port = 35357
auth_protocol = http
auth_uri = http://keystonehost:5000/
admin_tenant_name = service
admin_user = swift
admin_password = password
cache = swift.cache
include_service_catalog = False

The actual values for these variables will need to be set depending on your situation. For more information, please refer to the Keystone documentation on the auth_token middleware, but in short:

  • Those variables beginning with auth_ point to the Keystone Admin service. This information is used by the middleware to actually query Keystone about the validity of the authentication tokens.
  • The admin auth credentials (admin_user, admin_tenant_name, admin_password) will be used to retrieve an admin token. That token will be used to authorize user tokens behind the scenes.
  • cache is set to swift.cache. This means that the middleware will get the Swift memcache from the request environment.
  • include_service_catalog defaults to True if not set. This means that when validating a token, the service catalog is retrieved and stored in the X-Service-Catalog header. Since Swift does not use the X-Service-Catalog header, there is no point in getting the service catalog. We recommend you set include_service_catalog to False.

Note

If support is required for unvalidated users (as with anonymous access) or for tempurl/formpost middleware, authtoken will need to be configured with delay_auth_decision set to 1.

and you can finally add the keystoneauth configuration:

[filter:keystoneauth]
use = egg:swift#keystoneauth
operator_roles = admin, swiftoperator

By default the only users able to give ACL or to Create other containers are the ones who has the Keystone role specified in the operator_roles setting.

This user who have one of those role will be able to give ACLs to other users on containers, see the documentation on ACL here swift.common.middleware.acl.

Users with the Keystone role defined in reseller_admin_role (ResellerAdmin by default) can operate on any account. The auth system sets the request environ reseller_request to True if a request is coming from a user with this role. This can be used by other middlewares.

Extending Auth

TempAuth is written as wsgi middleware, so implementing your own auth is as easy as writing new wsgi middleware, and plugging it in to the proxy server. The KeyStone project and the Swauth project are examples of additional auth services.

Also, see Auth Server and Middleware.

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