Token authentication

The token auth method is built-in and is at the core of client authentication. Other auth methods may be used to authenticate a client, but they eventually result in the generation of a client token managed by the token backend.

Every token has a number of properties:

• ID - The primary ID of a token is a randomly generated value
• Display Name - Optionally, a human readable display name
• Metadata - Metadata used for audit logging
• Number of Uses - Optionally, a restricted use count
• Parent ID - Optionally, a parent token which created this child token
• Policies - An associated list of ACL policies
• Source Path - The path at which the token was generated (e.g. auth/github/login)

The properties of a token are immutable once created. The exception to this is the number of uses, which is decremented on each request. Each of these properties enable Vault to do a number of interesting things.

Each token maintains the source path, or the login path, that was used to create the token. This is used to allow source based revocation. For example, if we believe our GitHub organization was compromised, we may want to revoke all tokens generated via auth/github/login. This would be done by using the sys/revoke-prefix/ API with the auth/github/ prefix. Revoking the prefix will revoke all client tokens generated at that path, as well as all dynamic secrets generated by those tokens. This provides a powerful "break glass" procedure during a potential compromise.

If a token is created by another auth method, they do not have a parent token. However, any tokens created by the auth/token/create API have a parent token, namely the token used to make that request. By maintaining this parent-child relationship, Vault models token trees. Child tokens can be created with a subset of the parent policies, allowing for dropping of privileges. When a token is revoked, the entire sub-tree of tokens is revoked with it. This allows clients to safely generate child tokens and then revoke them all along with the root.

Child tokens are very useful, especially when combined with limited use tokens. When a token is created, its use count can be optionally specified. Providing a use count of one makes a one time token. This means the token can be used for a single request before being automatically revoked. This can be generalized to any number of uses. Limited use tokens cannot be used to create sub-tokens, but they can be a powerful way to allow extremely limited access to Vault.