Keystone tokens

Keystone tokens

Tokens are used to authenticate and authorize your interactions with the various OpenStack APIs. Tokens come in many scopes, representing various authorization and sources of identity.

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 providers, fernet and jws.

Fernet tokens

The fernet token format was introduced in the OpenStack Kilo release and now is the default token provider in Keystone. 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 Fernet - Frequently Asked Questions.

A deployment might consider using the fernet provider as opposed to JWS tokens if they are concerned about public expose of the payload used to build tokens.

JWS tokens

The JSON Web Signature (JWS) token format is a type of JSON Web Token (JWT) and it was implemented in the Stein release. JWS tokens are signed, meaning the information used to build the token ID is not opaque to users and can it can be decoded by anyone. JWS tokens are ephemeral, or non-persistent, which means they won’t bloat the database or require replication across nodes. Since the JWS token provider uses asymmetric keys, the tokens are signed with private keys and validated with public keys. The JWS token provider implementation only supports the ES256 JSON Web Algorithm (JWA), which is an Elliptic Curve Digital Signature Algorithm (ECDSA) using the P-256 curve and a SHA-256 hash algorithm.

A deployment might consider using JWS tokens as opposed to fernet tokens if there are security concerns about sharing symmetric encryption keys across hosts. Note that a major difference between the two providers is that JWS tokens are not opaque and can be decoded by anyone with the token ID. Fernet tokens are opaque in that the token ID is ciphertext. Despite the JWS token payload being readable by anyone, keystone reserves the right to make backwards incompatible changes to the token payload itself, which is not an API contract. We only recommend validating the token against keystone’s authentication API to inspect its associated metadata. We strongly discourage relying on decoded payloads for information about tokens.

More information about JWTs can be found in the specification.

Summary

Feature Status Fernet tokens JWS tokens
Create unscoped token mandatory
Create system-scoped token mandatory
Create project-scoped token mandatory
Create domain-scoped token optional
Create trust-scoped token optional
Create a token given an OAuth access token optional
Revoke a token optional

Details

  • Create unscoped token

    Status: mandatory.

    CLI commands:

    • openstack --os-username=<username> --os-user-domain-name=<domain> --os-password=<password> token issue

    Notes: All token providers must be capable of issuing tokens without an explicit scope of authorization.

    Driver Support:

    • Fernet tokens: complete
    • JWS tokens: complete

  • Create system-scoped token

    Status: mandatory.

    CLI commands:

    • openstack --os-username=<username> --os-user-domain-name=<domain> --os-system-scope all token issue

    Notes: All token providers must be capable of issuing system-scoped tokens.

    Driver Support:

    • Fernet tokens: complete
    • JWS tokens: complete

  • Create project-scoped token

    Status: mandatory.

    CLI commands:

    • openstack --os-username=<username> --os-user-domain-name=<domain> --os-password=<password> --os-project-name=<project> --os-project-domain-name=<domain> token issue

    Notes: All token providers must be capable of issuing project-scoped tokens.

    Driver Support:

    • Fernet tokens: complete
    • JWS tokens: complete

  • Create domain-scoped token

    Status: optional.

    CLI commands:

    • openstack --os-username=<username> --os-user-domain-name=<domain> --os-password=<password> --os-domain-name=<domain> token issue

    Notes: Domain-scoped tokens are not required for all use cases, and for some use cases, projects can be used instead.

    Driver Support:

    • Fernet tokens: complete
    • JWS tokens: complete

  • Create trust-scoped token

    Status: optional.

    CLI commands:

    • openstack --os-username=<username> --os-user-domain-name=<domain> --os-password=<password> --os-trust-id=<trust> token issue

    Notes: Tokens scoped to a trust convey only the user impersonation and project-based authorization attributes included in the delegation.

    Driver Support:

    • Fernet tokens: complete
    • JWS tokens: complete

  • Create a token given an OAuth access token

    Status: optional.

    Notes: OAuth access tokens can be exchanged for keystone tokens.

    Driver Support:

    • Fernet tokens: complete
    • JWS tokens: complete

  • Revoke a token

    Status: optional.

    CLI commands:

    • openstack token revoke

    Notes: Tokens may be individually revoked, such as when a user logs out of Horizon. Under certain circumstances, it’s acceptable for more than just a single token may be revoked as a result of this operation (such as when the revoked token was previously used to create additional tokens).

    Driver Support:

    • Fernet tokens: complete
    • JWS tokens: complete

Notes:

  • This document is a continuous work in progress
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