kuberos

An OIDC authentication helper for Kubernetes' kubectl.

Purpose

Kubernetes supports several authentication methods, a popular one of which is OIDC. The kubectl commandline tool can be configured to use OIDC authentication, including automatically refreshing its token on invocation. In order to enable this functionality kubectl must be configured with the following parameters:

• A client ID
• A client secret
• An issuer URL
• An ID token
• A refresh token

The latter two of these parameters must be aquired by performing an initial OIDC authentication outside of kubectl. OIDC is an awkward authentication method for a commandline tool as it is entirely browser based. Existing implementations (see Alternatives) provide CLI tools to handle this initial authentication. These CLIs will typically require the user connect to localhost in their Browser to perform the initial authentication.

Kuberos is designed to instead run as a hosted service. It authenticates users against an OIDC provider, returning a JSON payload of the parameters required by kubectl. Kuberos provides a simple frontend that links to a ~/.kube/config file generated from a supplied template of clusters. It also details how to manually add a user and context to a cluster, and how to use kubectl.

Usage

Before using Kuberos you must enable OIDC at the Kubernetes API server. Refer to this guide for details on how to get an OIDC client ID and secret from Google.

Kuberos is published to the Docker Hub. It must be configured with an OIDC issuer, client ID, and secret, as well as a partial kubeconfig file. For example:

export OIDC_CLIENT_ID=woo
export OIDC_CLIENT_SECRET=supersecret

echo $OIDC_CLIENT_SECRET >/tmp/cfg/secret
cat <<EOF >/tmp/cfg/template
apiVersion: v1
kind: Config
current-context: kuberos  # Optional - must be the name of one of the template's clusters.
clusters:
- name: kuberos
  cluster:
    certificate-authority-data: REDACTED
    server: https://kuberos.example.org
EOF

docker run -d -p 10003:10003 -v /tmp/cfg:/cfg "negz/kuberos:latest" \
  /kuberos https://accounts.google.com $OIDC_CLIENT_ID /cfg/secret /cfg/template

Kuberos supports the following arguments:

$ docker run negz/kuberos:latest /kuberos --help
usage: kuberos [<flags>] [<oidc-issuer-url>] [<client-id>] [<client-secret-file>] [<kubecfg-template>]

Provides OIDC authentication configuration for kubectl.

Flags:
      --help             Show context-sensitive help (also try --help-long and
                         --help-man).
      --listen=":10003"  Address at which to expose HTTP webhook.
  -d, --debug            Run with debug logging.
      --shutdown-grace-period=1m
                         Wait this long for sessions to end before shutting
                         down.

Args:
  [<oidc-issuer-url>]     OpenID Connect issuer URL.
  [<client-id>]           OAuth2 client ID.
  [<client-secret-file>]  File containing OAuth2 client secret.
  [<kubecfg-template>]    A kubecfg file containing clusters to populate with a
                          user and contexts.

The partial kubeconfig template should contain only cluster entries and optionally a current (i.e. default) context, which must be the name of one of the clusters. For example:

apiVersion: v1
kind: Config
current-context: staging
clusters:
- name: production
  cluster:
    certificate-authority-data: REDACTED
    server: https://prod.example.org
- name: staging
  cluster:
    certificate-authority-data: REDACTED
    server: https://staging.example.org

Given the above template Kuberos will generate a kubeconfig file containing the two supplied clusters, the authenticated OIDC user, and a context for each cluster associating them with the OIDC user. These contexts inherit the name of the clusters, thus a user could interact with the production cluster by running:

kubectl --context production cluster-info

If the current-context is set to the name of one of the clusters then the --context argument may be omitted, and the cluster named by current-context will be used.

Alternatives

OIDC helpers that run locally to setup kubectl:

• https://github.com/micahhausler/k8s-oidc-helper
• https://github.com/coreos/dex/tree/master/cmd/example-app

A Kubernetes JWT webhook helper with a similar UX to Kuberos

• https://github.com/negz/kubehook