11 KiB

Raw Blame History

Keystone for other services

This document provides a summary of some things that other services need to know about how keystone works, and specifically about how they can take advantage of the v3 API.

The v3 API was introduced as a stable API in the Grizzly release and included in the default pipeline ever since. Until recently, its use has been hidden from other services because the auth_token middleware translated the token format so that both versions look the same. Once the services need to make use of v3 features they need to know about how it works.

Glossary

Authentication: The process of determining if a user is who they claim to be (authN).
Authorization: The process of determining if a user can do what they are requesting (authZ).
Scope: A specific operating context. This is commonly used when describing the authorization a user may have. For example, a user with a role assignment on a project can get a token scoped to that project, ultimately operating within that project's scope.
System: An assignment target that refers to a collection of API services as a whole. Users and groups can be granted authorization on the deployment system.
Service: OpenStack services like identity, compute, image, etc.
Domain: A container for users, projects, and groups. A domain is also an assignment target for users and groups. It's possible for users and groups to have authorization on domains outside of the domain associated to their reference.
Project: A container and a namespace for resources isolated within OpenStack. A user, or group of users, must have a role assignment on a project in order to interact with it.
Token: A self-service resource that proves a user's identity and authentication. It can optionally carry a user's authorization, allowing them to interact with OpenStack services.
Role: A string that represents one or more permissions or capabilities.
Role Assignment: An association between an actor and a target that results in authorization. Actors can be users or groups of users. Targets can be projects, domains, or the deployment system itself.
User: A entity modeling an end-user of the system.
Group: A container for users. Users indirectly inherit any authorization the group has on projects, domains, or the system.

Domains

A major new feature in v3 is domains. Every project, user, and user group is owned by a domain (reflected by their domain_id value) which provides them their own namespace. For example, unlike in v2.0, usernames are no longer unique across the deployment. You can have two users with the same name, but they must be in different domains. However, user IDs are assigned to users by keystone and are expected to be unique across the deployment. All of this logic applies to projects, user groups and roles.

One of the great things about domains is that you can have one domain backed by SQL (for service users) and another backed by LDAP (the cloud is deployed into existing infrastructure).

The "default" domain

Note

The v2.0 API has been removed as of the Queens release. While this section references the v2.0 API, it is purely for historical reasons that clarify the existance of the default domain.

Domains were introduced as a v3-only feature. As a result, the v2.0 API didn't understand the concept of domains. To allow for both versions of the Identity API to run side-by-side, the idea of a default domain was established.

The default domain was a domain that was guaranteed to exist and was created during the keystone-manage db_sync process. By default, the domain ID is default and the name is Default, but it is possible to change these values through keystone's configuration file. The v2.0 API would consider users and projects existing within that domain as valid, but it would never expose domain information through the API. This allowed the v2.0 API to operate under the assumption that everything within the default domain was accessible. This was crucial in avoiding namespace conflicts between v2.0 and v3 where multiple domains existed. Using v3 allowed deployers the ability to experiment with domains, while isolating them from the v2.0 API.

As far as the v3 API is concerned, the default domain is simply a domain and doesn't carry any special connotation like it did with v2.0.

Authorization Scopes

End users use the Identity API as a way to express their authoritative power to other OpenStack services. This is done using tokens, which can be scoped to one of several targets depending on the users' role assignments. This is typically referred to as a token's scope. This happens when a user presents credentials, in some form or fashion, to keystone in addition to a desired scope. If keystone can prove the user is who they say they are (authN), it will then validate that the user has access to the scope they are requesting (authZ). If successful, the token response will contain a token ID and data about the transaction, such as the scope target and role assignments. Users can use this token ID in requests to other OpenStack services, which consume the authorization information associated to that token to make decisions about what that user can or cannot do within that service.

This section describes the various scopes available, and what they mean for services consuming tokens.

System Scope

A system-scoped token implies the user has authorization to act on the deployment system. These tokens are useful for interacting with resources that affect the deployment as a whole, or exposes resources that may otherwise violate project or domain isolation.

Good examples of system-scoped resources include:

Services: Service entities within keystone that describe the services deployed in a cloud.
Endpoints: Endpoints that tell users where to find services deployed in a cloud.
Hypervisors: Hosts for servers that belong to various projects.

Domain Scope

A domain-scoped token carries a user's authorization on a specific domain. Ideally, these tokens would be useful for listing resources aggregated across all projects with that domain. They can also be useful for creating entities that must belong to a domain. Users and groups are good examples of this. The following is an example of how a domain-scoped token could be used against a service.

Assume a domain exists called Foo. and it contains projects call bar and baz. Let's also assume both projects contain compute servers running a workload. If Alice is a domain administrator for Foo, she should be able to pass her domain-scoped token to nova and ask for a list of instances. If nova supports domain-scoped token, the response would contain all instances in projects bar and baz.

Another example of using a domain-scoped token would be if Alice wanted to create a new project in domain Foo. When Alice sends a request for keystone to create a project, keystone should ensure the new project is created within the Foo domain, since that's the authorization associated to Alice's token.

Warning

This behavior isn't completely implemented, and is still in progress. This example describes the ideal behavior, specifically for developers looking to implement scope into their APIs.

Project Scope

A project-scoped token carries the role assignments a user has on a project. This type of scope is great for managing resources that fit nicely within project boundaries. Good examples of project-level resources that can be managed with project-scoped tokens are:

Instances: Virtual compute servers that require a project association in order to be created.
Volumes: Storage devices that can be attached to instances.

Unscoped

An unscoped token is a token that proves authentication, but doesn't carry any authorization. Users can obtain unscoped tokens by simply proving their identity with credentials. Unscoped tokens can be exchanged for any of the various scoped tokens if a user has authorization on the requested scope.

An example of where unscoped tokens are specifically useful is when users perform federated authentication. First, a user will receive an unscoped token pending successful federated authentication, which they can use to query keystone for a list of projects they're allowed to access. Then they can exchange their unscoped token for a project-scoped token allowing them to perform actions within a particular project.

Auth Token middleware

The auth_token middleware handles token validation for the different services. Conceptually, what happens is that auth_token pulls the token out of the X-Auth-Token request header, validates the token using keystone, produces information about the identity (the API user) and authorization context (the project, roles, etc) of the token, and sets environment variables with that data. The services typically take the environment variables, put them in the service's "context", and use the context for policy enforcement via oslo.policy.

Service tokens

Service tokens are a feature where the auth_token middleware will also accept a service token in the X-Service-Token header. It does the same thing with the service token as the user token, but the results of the token are passed separately in environment variables for the service token (the service user, project, and roles). If the service knows about these then it can put this info in its "context" and use it for policy checks. For example, assuming there's a special policy rule called service_role that works like the role rule except checks the service roles, you could have an oslo.policy rule like service_role:service and user_id:%(user_id)s such that a service token is required along with the user owning the object.

Picking the version

Use version discovery to figure out what version the identity server supports rather than configuring the version. This will make it easier to adopt new API versions as they are implemented.

For information about how to accomplish service discovery with the keystoneauth library, please see the documentation.

Hierarchical Multitenancy

This feature is specific to v3 and allows projects to have parents, siblings, and children relationships with other projects.

Tokens scoped to projects in a hierarchical structure won't contain information about the hierarchy in the token response. If the service needs to know the hierarchy it should use the v3 API to fetch the hierarchy.

11 KiB Raw Blame History