Kubernetes auth method
Note: This engine can use external X.509 certificates as part of TLS or signature validation. Verifying signatures against X.509 certificates that use SHA-1 is deprecated and is no longer usable without a workaround starting in Vault 1.12. See the deprecation FAQ for more information.
The kubernetes
auth method can be used to authenticate with Vault using a
Kubernetes Service Account Token. This method of authentication makes it easy to
introduce a Vault token into a Kubernetes Pod.
You can also use a Kubernetes Service Account Token to log in via JWT auth. See the section on How to work with short-lived Kubernetes tokens for a summary of why you might want to use JWT auth instead and how it compares to Kubernetes auth.
Note: If you are upgrading to Kubernetes v1.21+, ensure the config option
disable_iss_validation
is set to true. Assuming the default mount path, you
can check with vault read -field disable_iss_validation auth/kubernetes/config
.
See Kubernetes 1.21 below for more details.
Authentication
Via the CLI
The default path is /kubernetes
. If this auth method was enabled at a
different path, specify -path=/my-path
in the CLI.
Via the API
The default endpoint is auth/kubernetes/login
. If this auth method was enabled
at a different path, use that value instead of kubernetes
.
The response will contain a token at auth.client_token
:
Configuration
Auth methods must be configured in advance before users or machines can authenticate. These steps are usually completed by an operator or configuration management tool.
Enable the Kubernetes auth method:
Use the
/config
endpoint to configure Vault to talk to Kubernetes. Usekubectl cluster-info
to validate the Kubernetes host address and TCP port. For the list of available configuration options, please see the API documentation.Note: The pattern Vault uses to authenticate Pods depends on sharing the JWT token over the network. Given the security model of Vault, this is allowable because Vault is part of the trusted compute base. In general, Kubernetes applications should not share this JWT with other applications, as it allows API calls to be made on behalf of the Pod and can result in unintended access being granted to 3rd parties.
Create a named role:
This role authorizes the "myapp" service account in the default namespace and it gives it the default policy.
For the complete list of configuration options, please see the API documentation.
Kubernetes 1.21
Starting in version 1.21, the Kubernetes
BoundServiceAccountTokenVolume
feature defaults to enabled. This changes the
JWT token mounted into containers by default in two ways that are important for
Kubernetes auth:
- It has an expiry time and is bound to the lifetime of the pod and service account.
- The value of the JWT's
"iss"
claim depends on the cluster's configuration.
The changes to token lifetime are important when configuring the
token_reviewer_jwt
option.
If a short-lived token is used,
Kubernetes will revoke it as soon as the pod or service account are deleted, or
if the expiry time passes, and Vault will no longer be able to use the
TokenReview
API. See How to work with short-lived Kubernetes tokens
below for details on handling this change.
In response to the issuer changes, Kubernetes auth has been updated in Vault
1.9.0 to not validate the issuer by default. The Kubernetes API does the same
validation when reviewing tokens, so enabling issuer validation on the Vault
side is duplicated work. Without disabling Vault's issuer validation, it is not
possible for a single Kubernetes auth configuration to work for default mounted
pod tokens with both Kubernetes 1.20 and 1.21. Note that auth mounts created
before Vault 1.9 will maintain the old default, and you will need to explicitly
set disable_iss_validation=true
before upgrading Kubernetes to 1.21. See
Discovering the service account issuer
below for guidance if you wish to enable issuer validation in Vault.
How to work with short-lived kubernetes tokens
There are a few different ways to configure auth for Kubernetes pods when default mounted pod tokens are short-lived, each with their own tradeoffs. This table summarizes the options, each of which is explained in more detail below.
Option | All tokens are short-lived | Can revoke tokens early | Other considerations |
---|---|---|---|
Use local token as reviewer JWT | Yes | Yes | Requires Vault (1.9.3+) to be deployed on the Kubernetes cluster |
Use client JWT as reviewer JWT | Yes | Yes | Operational overhead |
Use long-lived token as reviewer JWT | No | Yes | |
Use JWT auth instead | Yes | No |
Note: By default, Kubernetes currently extends the lifetime of admission
injected service account tokens to a year to help smooth the transition to
short-lived tokens. If you would like to disable this, set
--service-account-extend-token-expiration=false for
kube-apiserver
or specify your own serviceAccountToken
volume mount. See
here for an example.
Use local service account token as the reviewer JWT
When running Vault in a Kubernetes pod the recommended option is to use the pod's local
service account token. Vault will periodically re-read the file to support
short-lived tokens. To use the local token and CA certificate, omit
token_reviewer_jwt
and kubernetes_ca_cert
when configuring the auth method.
Vault will attempt to load them from token
and ca.crt
respectively inside
the default mount folder /var/run/secrets/kubernetes.io/serviceaccount/
.
Note: Requires Vault 1.9.3+. In earlier versions the service account
token and CA certificate is read once and stored in Vault storage.
When the service account token expires or is revoked, Vault will no longer be
able to use the TokenReview
API and client authentication will fail.
Use the Vault client's JWT as the reviewer JWT
When configuring Kubernetes auth, you can omit the token_reviewer_jwt
, and Vault
will use the Vault client's JWT as its own auth token when communicating with
the Kubernetes TokenReview
API. If Vault is running in Kubernetes, you also need
to set disable_local_ca_jwt=true
.
This means Vault does not store any JWTs and allows you to use short-lived tokens
everywhere but adds some operational overhead to maintain the cluster role
bindings on the set of service accounts you want to be able to authenticate with
Vault. Each client of Vault would need the system:auth-delegator
ClusterRole:
Continue using long-lived tokens
You can create a long-lived secret using the instructions here
and use that as the token_reviewer_jwt
. In this example, the vault
service
account would need the system:auth-delegator
ClusterRole:
Using this maintains previous workflows but does not benefit from the improved security posture of short-lived tokens.
Use JWT auth
Kubernetes auth is specialized to use Kubernetes' TokenReview
API. However, the
JWT tokens Kubernetes generates can also be verified using Kubernetes as an OIDC
provider. The JWT auth method documentation has instructions for
setting up JWT auth with Kubernetes as the OIDC provider.
This solution allows you to use short-lived tokens for all clients and removes the need for a reviewer JWT. However, the client tokens cannot be revoked before their TTL expires, so it is recommended to keep the TTL short with that limitation in mind.
Discovering the service account issuer
Note: From Vault 1.9.0, disable_iss_validation
and issuer
are deprecated
and the default for disable_iss_validation
has changed to true
for new
Kubernetes auth mounts. The following section only applies if you have set
disable_iss_validation=false
or created your mount before 1.9 with the default
value, but disable_iss_validation=true
is the new recommended value for all
versions of Vault.
Kubernetes 1.21+ clusters may require setting the service account
issuer
to the same value as
kube-apiserver
's --service-account-issuer
flag. This is because the service
account JWTs for these clusters may have an issuer specific to the cluster
itself, instead of the old default of kubernetes/serviceaccount
. If you are
unable to check this value directly, you can run the following and look for the
"iss"
field to find the required value:
Most clusters will also have that information available at the
.well-known/openid-configuration
endpoint:
This value is then used when configuring Kubernetes auth, e.g.:
Configuring kubernetes
This auth method accesses the Kubernetes TokenReview API to
validate the provided JWT is still valid. Kubernetes should be running with
--service-account-lookup
. This is defaulted to true from Kubernetes 1.7.
Otherwise deleted tokens in Kubernetes will not be properly revoked and
will be able to authenticate to this auth method.
Service Accounts used in this auth method will need to have access to the TokenReview API. If Kubernetes is configured to use RBAC roles, the Service Account should be granted permissions to access this API. The following example ClusterRoleBinding could be used to grant these permissions:
API
The Kubernetes Auth Plugin has a full HTTP API. Please see the API docs for more details.
Code example
The following example demonstrates the Kubernetes auth method to authenticate with Vault.