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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-token-faq
.
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.