Kubernetes Auth Method

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.

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.

$ vault write auth/kubernetes/login role=demo jwt=...

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.

$ curl \
    --request POST \
    --data '{"jwt": "<your service account jwt>", "role": "demo"}' \
    http://127.0.0.1:8200/v1/auth/kubernetes/login

The response will contain a token at auth.client_token:

{
  "auth": {
    "client_token": "38fe9691-e623-7238-f618-c94d4e7bc674",
    "accessor": "78e87a38-84ed-2692-538f-ca8b9f400ab3",
    "policies": ["default"],
    "metadata": {
      "role": "demo",
      "service_account_name": "vault-auth",
      "service_account_namespace": "default",
      "service_account_secret_name": "vault-auth-token-pd21c",
      "service_account_uid": "aa9aa8ff-98d0-11e7-9bb7-0800276d99bf"
    },
    "lease_duration": 2764800,
    "renewable": true
  }
}

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.

1. Enable the Kubernetes auth method:

   $ vault auth enable kubernetes
   

2. Use the /config endpoint to configure Vault to talk to Kubernetes. Use kubectl cluster-info to validate the Kubernetes host address and TCP port. For the list of available configuration options, please see the API documentation.

   $ vault write auth/kubernetes/config \
       token_reviewer_jwt="<your reviewer service account JWT>" \
       kubernetes_host=https://192.168.99.100:<your TCP port or blank for 443> \
       kubernetes_ca_cert=@ca.crt
   

   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.

3. Create a named role:

   vault write auth/kubernetes/role/demo \
       bound_service_account_names=vault-auth \
       bound_service_account_namespaces=default \
       policies=default \
       ttl=1h
   

   This role authorizes the "vault-auth" 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.

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 in Kubernetes 1.7, but any versions prior should ensure the Kubernetes API server is started with this setting. 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:

apiVersion: rbac.authorization.k8s.io/v1beta1
kind: ClusterRoleBinding
metadata:
  name: role-tokenreview-binding
  namespace: default
roleRef:
  apiGroup: rbac.authorization.k8s.io
  kind: ClusterRole
  name: system:auth-delegator
subjects:
  - kind: ServiceAccount
    name: vault-auth
    namespace: default

API

The Kubernetes Auth Plugin has a full HTTP API. Please see the API docs for more details.