The Auth System

this page last updated: 2018-04-18 02:06:40

The Auth System¶

Overview¶

Swift supports a number of auth systems that share the following common characteristics:

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 time in seconds from now. To avoid the overhead in validating the same token over and over again, Swift will cache the token for a configurable time, but no longer than the expiration time.

The Swift project includes two auth systems:

TempAuth
Keystone Auth

It is also possible to write your own auth system as described in Extending Auth.

TempAuth¶

TempAuth is used primarily in Swift’s functional test environment and can be used in other test environments (such as SAIO - Swift All In One). It is not recommended to use TempAuth in a production system. However, TempAuth is fully functional and can be used as a model to develop your own auth system.

TempAuth 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 read operations. However, some privileged metadata such as X-Container-Sync-Key is not accessible to non-admin users.

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.

Other users may be granted the ability to perform operations on an account or container via ACLs. TempAuth supports two types of ACL:

Per container ACLs based on the container’s X-Container-Read and X-Container-Write metadata. See Container ACLs for more information.
Per account ACLs based on the account’s X-Account-Access-Control metadata. For more information see Account ACLs.

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

The TempAuth middleware is responsible for creating its own tokens. A user makes a request containing their username and password and TempAuth responds with a token. This token is then used to perform subsequent requests on the user’s account, containers and objects.

Keystone Auth¶

Swift is able to authenticate against OpenStack Keystone. In this environment, Keystone is responsible for creating and validating tokens. The KeystoneAuth middleware is responsible for implementing the auth system within Swift as described here.

The KeystoneAuth middleware supports per container based ACLs on the container’s X-Container-Read and X-Container-Write metadata. For more information see Container ACLs.

The account-level ACL is not supported by Keystone auth.

In order to use the keystoneauth middleware the auth_token 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 straightforward. The first step is to ensure that you have the auth_token middleware installed. It can either be dropped in your python path or installed via the KeystoneMiddleware 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
www_authenticate_uri = http://keystonehost:5000/
auth_url = http://keystonehost:35357/
auth_plugin = password
project_domain_id = default
user_domain_id = default
project_name = service
username = swift
password = password
cache = swift.cache
include_service_catalog = False
delay_auth_decision = True

The actual values for these variables will need to be set depending on your situation, but in short:

www_authenticate_uri should point to a Keystone service from which users may retrieve tokens. This value is used in the WWW-Authenticate header that auth_token sends with any denial response.
auth_url points to the Keystone Admin service. This information is used by the middleware to actually query Keystone about the validity of the authentication tokens. It is not necessary to append any Keystone API version number to this URI.
The auth credentials (project_domain_id, user_domain_id, username, project_name, password) will be used to retrieve an admin token. That token will be used to authorize user tokens behind the scenes. These credentials must match the Keystone credentials for the Swift service. The example values shown here assume a user named ‘swift’ with admin role on a project named ‘service’, both being in the Keystone domain with id ‘default’. Refer to the KeystoneMiddleware documentation for other examples.
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

The authtoken config variable delay_auth_decision must be set to True. The default is False, but that breaks public access, StaticWeb, FormPost, TempURL, and authenticated capabilities requests (using Discoverability).

and you can finally add the keystoneauth configuration. Here is a simple configuration:

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

Use an appropriate list of roles in operator_roles. For example, in some systems, the role _member_ or Member is used to indicate that the user is allowed to operate on project resources.

OpenStack Service Using Composite Tokens¶

Some OpenStack services such as Cinder and Glance may use a “service account”. In this mode, you configure a separate account where the service stores project data that it manages. This account is not used directly by the end-user. Instead, all access is done through the service.

To access the “service” account, the service must present two tokens: one from the end-user and another from its own service user. Only when both tokens are present can the account be accessed. This section describes how to set the configuration options to correctly control access to both the “normal” and “service” accounts.

In this example, end users use the AUTH_ prefix in account names, whereas services use the SERVICE_ prefix:

[filter:keystoneauth]
use = egg:swift#keystoneauth
reseller_prefix = AUTH, SERVICE
operator_roles = admin, swiftoperator
SERVICE_service_roles = service

The actual values for these variable will need to be set depending on your situation as follows:

The first item in the reseller_prefix list must match Keystone’s endpoint (see /etc/keystone/default_catalog.templates above). Normally this is AUTH.
The second item in the reseller_prefix list is the prefix used by the OpenStack services(s). You must configure this value (SERVICE in the example) with whatever the other OpenStack service(s) use.
Set the operator_roles option to contain a role or roles that end-user’s have on project’s they use.
Set the SERVICE_service_roles value to a role or roles that only the OpenStack service user has. Do not use a role that is assigned to “normal” end users. In this example, the role service is used. The service user is granted this role to a single project only. You do not need to make the service user a member of every project.

This configuration works as follows:

The end-user presents a user token to an OpenStack service. The service then makes a Swift request to the account with the SERVICE prefix.
The service forwards the original user token with the request. It also adds it’s own service token.
Swift validates both tokens. When validated, the user token gives the admin or swiftoperator role(s). When validated, the service token gives the service role.
Swift interprets the above configuration as follows:
- Did the user token provide one of the roles listed in operator_roles?
- Did the service token have the service role as described by the SERVICE_service_roles options.
If both conditions are met, the request is granted. Otherwise, Swift rejects the request.

In the above example, all services share the same account. You can separate each service into its own account. For example, the following provides a dedicated account for each of the Glance and Cinder services. In addition, you must assign the glance_service and cinder_service to the appropriate service users:

[filter:keystoneauth]
use = egg:swift#keystoneauth
reseller_prefix = AUTH, IMAGE, VOLUME
operator_roles = admin, swiftoperator
IMAGE_service_roles = glance_service
VOLUME_service_roles = cinder_service

Access control using keystoneauth¶

By default the only users able to perform operations (e.g. create a container) on an account are those having a Keystone role for the corresponding Keystone project that matches one of the roles specified in the operator_roles option.

Users who have one of the operator_roles will be able to set container ACLs to grant other users permission to read and/or write objects in specific containers, using X-Container-Read and X-Container-Write headers respectively. In addition to the ACL formats described here, keystoneauth supports ACLs using the format:

other_project_id:other_user_id.

where other_project_id is the UUID of a Keystone project and other_user_id is the UUID of a Keystone user. This will allow the other user to access a container provided their token is scoped on the other project. Both other_project_id and other_user_id may be replaced with the wildcard character * which will match any project or user respectively.

Be sure to use Keystone UUIDs rather than names in container ACLs.

Note

For backwards compatibility, keystoneauth will by default grant container ACLs expressed as other_project_name:other_user_name (i.e. using Keystone names rather than UUIDs) in the special case when both the other project and the other user are in Keystone’s default domain and the project being accessed is also in the default domain.

For further information see KeystoneAuth

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.

Troubleshooting tips for keystoneauth deployment¶

Some common mistakes can result in API requests failing when first deploying keystone with Swift:

Incorrect configuration of the Swift endpoint in the Keystone service.

By default, keystoneauth expects the account part of a URL to have the form AUTH_<keystone_project_id>. Sometimes the AUTH_ prefix is missed when configuring Swift endpoints in Keystone, as described in the Install Guide. This is easily diagnosed by inspecting the proxy-server log file for a failed request URL and checking that the URL includes the AUTH_ prefix (or whatever reseller prefix may have been configured for keystoneauth):
```
GOOD:
proxy-server: 127.0.0.1 127.0.0.1 07/Sep/2016/16/06/58 HEAD /v1/AUTH_cfb8d9d45212408b90bc0776117aec9e HTTP/1.0 204 ...

BAD:
proxy-server: 127.0.0.1 127.0.0.1 07/Sep/2016/16/07/35 HEAD /v1/cfb8d9d45212408b90bc0776117aec9e HTTP/1.0 403 ...
```
Incorrect configuration of the authtoken middleware options in the Swift proxy server.

The authtoken middleware communicates with the Keystone service to validate tokens that are presented with client requests. To do this authtoken must authenticate itself with Keystone using the credentials configured in the [filter:authtoken] section of /etc/swift/proxy-server.conf. Errors in these credentials can result in authtoken failing to validate tokens and may be revealed in the proxy server logs by a message such as:
```
proxy-server: Identity server rejected authorization
```
Note

More detailed log messaging may be seen by setting the authtoken option log_level = debug.

The authtoken configuration options may be checked by attempting to use them to communicate directly with Keystone using an openstack command line. For example, given the authtoken configuration sample shown in Configuring Swift to use Keystone, the following command should return a service catalog:
```
openstack --os-identity-api-version=3 --os-auth-url=http://keystonehost:5000/ \
    --os-username=swift --os-user-domain-id=default \
    --os-project-name=service --os-project-domain-id=default \
    --os-password=password catalog show object-store
```
If this openstack command fails then it is likely that there is a problem with the authtoken configuration.

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 Swauth project is an example of an additional auth service.

See Auth Server and Middleware for detailed information on extending the auth system.