keystone/doc/source/admin/identity-tokens.rst

Keystone tokens

Tokens are used to authenticate and authorize your interactions with the various OpenStack APIs. Tokens come in many flavors, representing various authorization scopes and sources of identity. There are also several different "token providers", each with their own user experience, performance, and deployment characteristics.

Authorization scopes

Tokens are used to relay information about your user's role assignments. It's not uncommon for a user to have multiple role assignments, sometimes spanning projects, domains, or the entire system. These are referred to as authorization scopes, where a token has a single scope of operation. For example, a token scoped to a project can't be reused to do something else in a different project.

Each level of authorization scope is useful for certain types of operations in certain OpenStack services, and are not interchangeable.

Unscoped tokens

An unscoped token contains neither a service catalog, any roles, a project scope, nor a domain scope. Their primary use case is simply to prove your identity to keystone at a later time (usually to generate scoped tokens), without repeatedly presenting your original credentials.

The following conditions must be met to receive an unscoped token:

• You must not specify an authorization scope in your authentication request (for example, on the command line with arguments such as --os-project-name or --os-domain-id),
• Your identity must not have a "default project" associated with it that you also have role assignments, and thus authorization, upon.

Project-scoped tokens

Project-scoped tokens express your authorization to operate in a specific tenancy of the cloud and are useful to authenticate yourself when working with most other services.

They contain a service catalog, a set of roles, and details of the project upon which you have authorization.

Domain-scoped tokens

Domain-scoped tokens have limited use cases in OpenStack. They express your authorization to operate a domain-level, above that of the user and projects contained therein (typically as a domain-level administrator). Depending on Keystone's configuration, they are useful for working with a single domain in Keystone.

They contain a limited service catalog (only those services which do not explicitly require per-project endpoints), a set of roles, and details of the project upon which you have authorization.

They can also be used to work with domain-level concerns in other services, such as to configure domain-wide quotas that apply to all users or projects in a specific domain.

System-scoped tokens

There are APIs across OpenStack that fit nicely within the concept of a project or domain, but there are also APIs that affect the entire deployment system (e.g. modifying endpoints, service management, or listing information about hypervisors). These operations require the use of a system-scoped token, which represents the role assignments a user has to operate on the deployment as a whole.

Token providers

The token type issued by keystone is configurable through the /etc/keystone/keystone.conf file. Currently, there are two supported token types, UUID and fernet.

UUID tokens

UUID was the first token type supported and is currently the default token provider. UUID tokens are 32 bytes in length and must be persisted in a back end. Clients must pass their UUID token to the Identity service in order to validate it.

As mentioned above, UUID tokens must be persisted. By default, keystone persists UUID tokens using a SQL backend. An unfortunate side-effect is that the size of the database will grow over time regardless of the token's expiration time. Expired UUID tokens can be pruned from the backend using keystone's command line utility:

$ keystone-manage token_flush

We recommend invoking this command periodically using cron.

Note

It is not required to run this command at all if using Fernet tokens. Fernet tokens are not persisted and do not contribute to database bloat.

Fernet tokens

The fernet token format was introduced in the OpenStack Kilo release. Unlike the other token types mentioned in this document, fernet tokens do not need to be persisted in a back end. AES256 encryption is used to protect the information stored in the token and integrity is verified with a SHA256 HMAC signature. Only the Identity service should have access to the keys used to encrypt and decrypt fernet tokens. Like UUID tokens, fernet tokens must be passed back to the Identity service in order to validate them. For more information on the fernet token type, see the identity-fernet-token-faq.