Traefik Forward Auth using Google Oauth2 for SSO

Traefik Forward Auth is incredibly useful to secure services with an additional layer of authentication, provided by an OIDC-compatible provider. The simplest possible provider is a self-hosted instance of Dex, configured with a static username and password. This is not much use if you want to provide "normies" access to your services though - a better solution would be to validate their credentials against an existing trusted public source.

This recipe will illustrate how to point Traefik Forward Auth to Google, confirming that the requestor has a valid Google account (and that said account is permitted to access your services!)

Ingredients

Preparation

Obtain OAuth credentials

TL;DR

Log into https://console.developers.google.com/, create a new project then search for and select "Credentials" in the search bar.

Fill out the "OAuth Consent Screen" tab, and then click, "Create Credentials" > "OAuth client ID". Select "Web Application", fill in the name of your app, skip "Authorized JavaScript origins" and fill "Authorized redirect URIs" with either all the domains you will allow authentication from, appended with the url-path (e.g. https://radarr.example.com/_oauth, https://radarr.example.com/_oauth, etc), or if you don't like frustration, use a "auth host" URL instead, like "https://auth.example.com/_oauth" (see below for details)

Monkey see, monkey do 🙈

Here's a screencast I recorded of the OIDC credentias setup in Google Developer Console

Prepare {{ no such element: dict object['recipe'] }} environment

Create /var/data/config/traefik-forward-auth/traefik-forward-auth.env as per the following example:

PROVIDERS_GOOGLE_CLIENT_ID=<your client id>
PROVIDERS_GOOGLE_CLIENT_SECRET=<your client secret>
SECRET=<a random string, make it up>
# comment out AUTH_HOST if you'd rather use individual redirect_uris (slightly less complicated but more work)
AUTH_HOST=auth.example.com
COOKIE_DOMAINS=example.com
WHITELIST=you@yourdomain.com, me@mydomain.com 

Prepare the docker service config

Create /var/data/config/traefik-forward-auth/traefik-forward-auth.yml as per the following example:

  traefik-forward-auth:
    image: thomseddon/traefik-forward-auth:2.1.0
    env_file: /var/data/config/traefik-forward-auth/traefik-forward-auth.env
    networks:
      - traefik_public
    deploy:
      labels # you only need these if you're using an auth host
        # traefik
        - traefik.enable=true
        - traefik.docker.network=traefik_public

        # traefikv1
        - "traefik.port=4181"
        - "traefik.frontend.rule=Host:auth.example.com"
        - "traefik.frontend.auth.forward.address=http://traefik-forward-auth:4181"
        - "traefik.frontend.auth.forward.trustForwardHeader=true"

        # traefikv2
        - "traefik.docker.network=traefik_public"
        - "traefik.http.routers.auth.rule=Host(`auth.example.com`)"
        - "traefik.http.routers.auth.entrypoints=https"
        - "traefik.http.routers.auth.tls=true"
        - "traefik.http.routers.auth.tls.domains[0].main=example.com"
        - "traefik.http.routers.auth.tls.domains[0].sans=*.example.com"        
        - "traefik.http.routers.auth.tls.certresolver=main"
        - "traefik.http.routers.auth.service=auth@docker"
        - "traefik.http.services.auth.loadbalancer.server.port=4181"
        - "traefik.http.middlewares.forward-auth.forwardauth.address=http://traefik-forward-auth:4181"
        - "traefik.http.middlewares.forward-auth.forwardauth.trustForwardHeader=true"
        - "traefik.http.middlewares.forward-auth.forwardauth.authResponseHeaders=X-Forwarded-User"
        - "traefik.http.routers.auth.middlewares=forward-auth"

If you're not confident that forward authentication is working, add a simple "whoami" test container to the above .yml, to help debug traefik forward auth, before attempting to add it to a more complex container.

  # This simply validates that traefik forward authentication is working
  whoami:
    image: containous/whoami
    networks:
      - traefik_public
    deploy:
      labels:
        # traefik
        - traefik.enable=true
        - traefik.docker.network=traefik_public

        # traefikv1
        - traefik.frontend.rule=Host:whoami.example.com
        - "traefik.http.services.linx.loadbalancer.server.port=80"
        - traefik.frontend.auth.forward.address=http://traefik-forward-auth:4181
        - traefik.frontend.auth.forward.authResponseHeaders=X-Forwarded-User
        - traefik.frontend.auth.forward.trustForwardHeader=true        

        # traefikv2
        - "traefik.http.routers.whoami.rule=Host(`whoami.example.com`)"
        - "traefik.http.routers.whoami.entrypoints=https"
        - "traefik.http.services.whoami.loadbalancer.server.port=80"
        - "traefik.http.routers.whoami.middlewares=forward-auth" # this line enforces traefik-forward-auth  

Serving

Launch

Deploy traefik-forward-auth with docker stack deploy traefik-forward-auth -c /var/data/traefik-forward-auth/traefik-forward-auth.yml

Test

Browse to https://whoami.example.com (obviously, customized for your domain and having created a DNS record), and all going according to plan, you should be redirected to a Google login. Once successfully logged in, you'll be directed to the basic whoami page.

Summary

What have we achieved? By adding an additional three simple labels to any service, we can secure any service behind our choice of OAuth provider, with minimal processing / handling overhead.

Chef's notes 📓

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