dex/Documentation/kubernetes.md

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# Kubernetes authentication through dex
## Overview
This document covers setting up the [Kubernetes OpenID Connect token authenticator plugin][k8s-oidc] with dex.
Token responses from OpenID Connect providers include a signed JWT called an ID Token. ID Tokens contain names, emails, unique identifiers, and in dex's case, a set of groups that can be used to identify the user. OpenID Connect providers, like dex, publish public keys; the Kubernetes API server understands how to use these to verify ID Tokens.
The authentication flow looks like:
1. OAuth2 client logs a user in through dex.
2. That client uses the returned ID Token as a bearer token when talking to the Kubernetes API.
3. Kubernetes uses dex's public keys to verify the ID Token.
4. A claim designated as the username (and optionally group information) will be associated with that request.
Username and group information can be combined with Kubernetes [authorization plugins][k8s-authz], such as roles based access control (RBAC), to enforce policy.
## Configuring the OpenID Connect plugin
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Configuring the API server to use the OpenID Connect [authentication plugin][k8s-oidc] requires:
* Deploying an API server with specific flags.
* Dex is running on HTTPS.
* Custom CA files must be accessible by the API server (likely through volume mounts).
* Dex is accessible to both your browser and the Kubernetes API server.
Use the following flags to point your API server(s) at dex. `dex.example.com` should be replaced by whatever DNS name or IP address dex is running under.
```
--oidc-issuer-url=https://dex.example.com:32000
--oidc-client-id=example-app
--oidc-ca-file=/etc/kubernetes/ssl/openid-ca.pem
--oidc-username-claim=email
--oidc-groups-claim=groups
```
Additional notes:
* The API server configured with OpenID Connect flags doesn't require dex to be available upfront.
* Other authenticators, such as client certs, can still be used.
* Dex doesn't need to be running when you start your API server.
* Kubernetes only trusts ID Tokens issued to a single client.
* As a work around dex allows clients to [trust other clients][trusted-peers] to mint tokens on their behalf.
* If a claim other than "email" is used for username, for example "sub", it will be prefixed by `"(value of --oidc-issuer-url)#"`. This is to namespace user controlled claims which may be used for privilege escalation.
## Deploying dex on Kubernetes
The dex repo contains scripts for running dex on a Kubernetes cluster with authentication through GitHub. The dex service is exposed using a [node port][node-port] on port 32000. This likely requires a custom `/etc/hosts` entry pointed at one of the cluster's workers.
Because dex uses `ThirdPartyResources` to store state, no external database is needed. For more details see the [storage documentation](storage.md#kubernetes-third-party-resources).
There are many different ways to spin up a Kubernetes development cluster, each with different host requirements and support for API server reconfiguration. At this time, this guide does not have copy-pastable examples, but can recommend the following methods for spinning up a cluster:
* [coreos-kubernetes][coreos-kubernetes] repo for vagrant and VirtualBox users.
* [coreos-baremetal][coreos-baremetal] repo for Linux QEMU/KVM users.
To run dex on Kubernetes perform the following steps:
1. Generate TLS assets for dex.
2. Spin up a Kubernetes cluster with the appropriate flags and CA volume mount.
3. Create a secret containing your [GitHub OAuth2 client credentials][github-oauth2].
4. Deploy dex.
5. Create and assign 'dex' cluster role to dex service account (if RBAC authorization is used).
The TLS assets can be created using the following command:
```
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$ cd examples/k8s
$ ./gencert.sh
```
The created `ssl/ca.pem` must then be mounted into your API server deployment. Once the cluster is up and correctly configured, use kubectl to add the serving certs as secrets.
```
$ kubectl create secret tls dex.example.com.tls --cert=ssl/cert.pem --key=ssl/key.pem
```
Then create a secret for the GitHub OAuth2 client.
```
$ kubectl create secret \
generic github-client \
--from-literal=client-id=$GITHUB_CLIENT_ID \
--from-literal=client-secret=$GITHUB_CLIENT_SECRET
```
Create the dex deployment, configmap, and node port service.
```
$ kubectl create -f dex.yaml
```
Assign cluster role to dex service account so it can create third party resources [Kubernetes third party resources](storage.md).
__Caveats:__ No health checking is configured because dex does its own TLS termination complicating the setup. This is a known issue and can be tracked [here][dex-healthz].
## Logging into the cluster
The `example-app` can be used to log into the cluster and get an ID Token. To build the app, you can run `make` in the root of the repo and it will build the `example-app` binary in the repo's `bin` directory. To build the `example-app` requires at least a 1.7 version of Go.
```
$ ./bin/example-app --issuer https://dex.example.com:32000 --issuer-root-ca examples/k8s/ssl/ca.pem
```
Please note that the `example-app` will listen at http://127.0.0.1:5555 and can be changed with the `--listen` flag.
Once the example app is running, choose the GitHub option and grant access to dex to view your profile.
The default redirect uri is http://127.0.0.1:5555/callback and can be changed with the `--redirect-uri` flag and should correspond with your configmap.
The printed ID Token can then be used as a bearer token to authenticate against the API server.
```
$ token='(id token)'
$ curl -H "Authorization: Bearer $token" -k https://( API server host ):443/api/v1/nodes
```
[k8s-authz]: http://kubernetes.io/docs/admin/authorization/
[k8s-oidc]: http://kubernetes.io/docs/admin/authentication/#openid-connect-tokens
[trusted-peers]: https://godoc.org/github.com/dexidp/dex/storage#Client
[coreos-kubernetes]: https://github.com/coreos/coreos-kubernetes/
[coreos-baremetal]: https://github.com/coreos/coreos-baremetal/
[dex-healthz]: https://github.com/dexidp/dex/issues/682
[github-oauth2]: https://github.com/settings/applications/new
[node-port]: http://kubernetes.io/docs/user-guide/services/#type-nodeport
[coreos-kubernetes]: https://github.com/coreos/coreos-kubernetes
[coreos-baremetal]: https://github.com/coreos/coreos-baremetal