Traefik OIDC Relying Party

(fork of https://github.com/Gwojda/keycloakopenid)

This plugin for Traefik allows it to authenticate requests against an OpenID Provider like Zitadel, Keycloak, Authentik, etc. (I test it with Zitadel, my homelab's IAM solution). It utilizes the provider's client credentials flow to retrieve an access token, which is then set as a bearer token in the Authorization header of the incoming requests. The plugin communicates with the provider using the OpenID Connect protocol (OIDC).

Code Explanation

Structs

The plugin uses several data structures:

Config: This struct stores the configuration details of the Provider instance, such as the URL, client ID, and client secret.
ProviderAuth: This struct is the main component of the plugin, storing the next HTTP handler and the configuration.
ProviderTokenResponse: This struct stores the response from the Provider when a token is requested.
state: This struct stores the URL to which the user should be redirected after successful authentication.

Main Functions

The plugin has several main functions:

CreateConfig(): Initializes and returns a new Config struct.
New(): Creates a new Provider authentication middleware. It checks the provided configuration and returns an error if the Provider URL or client ID is not provided.
ServeHTTP(): This is the main function of the middleware. It checks for an "Authorization" cookie in the request. If the cookie exists and its value starts with "Bearer ", it verifies the token. If the token is valid, it allows the request to proceed. If the token is invalid, it redirects the request to the Provider for authentication. If the cookie does not exist, it checks for an authorization code in the request URL. If the code exists, it exchanges it for a token. If the code does not exist, it redirects the request to the Provider for authentication.
exchangeAuthCode(): Exchanges an authorization code for a token.
redirectToProvider(): Redirects the request to the Provider for authentication.
verifyToken(): Verifies the validity of a token.

How it Works

When a request is received, the middleware first checks for an "Authorization" cookie. If it exists and the token inside is valid, the request is allowed to proceed. If the token is invalid or doesn't exist, the middleware checks for an authorization code in the request URL. If the authorization code exists, the middleware exchanges it for a token, sets this token as a cookie, and redirects the user to their original location. If the authorization code doesn't exist, the middleware redirects the user to the Provider for authentication. The user is then prompted to enter their credentials on the Provider login page. After successful authentication, the Provider redirects the user back to the application with an authorization code. The middleware then exchanges this code for a token and the process starts over. By using this middleware, applications can easily integrate with the Provider for user authentication without having to implement the logic themselves.

Installation

First, enable the plugins support in your Traefik configuration file (traefik.yml or traefik.toml):

experimental:
  plugins:
    traefik-oidc-relying-party:
      moduleName: "github.com/alexdelprete/traefik-oidc-relying-party"
      version: "v1.0.0"

Usage Add the plugin's specific configuration to your Traefik routers:

http:
  middlewares:
    oidc-auth:
      plugin:
        traefik-oidc-relying-party:
          ProviderURL: "https://my-provider-url.com"
          ClientID: "<CLIENT_ID>"
          ClientSecret: "<CLIENT_SECRET>"

Alternatively, ClientID and ClientSecret can be read from a file to support Docker Secrets and Kubernetes Secrets:

http:
  middlewares:
    my-provider-openid:
      plugin:
        traefik-oidc-relying-party:
          ProviderURL: "https://my-provider-url.com/auth"
          ClientIDFile: "/run/secrets/clientId.txt"
          ClientSecretFile: "/run/secrets/clientSecret.txt"

Last but not least, each configuration can be read from environment file to support some Kubernetes configurations:

http:
  middlewares:
    my-provider-openid:
      plugin:
        traefik-oidc-relying-party:
          ProviderURLEnv: "MY_PROVIDER_URL"
          ClientIDEnv: "MY_PROVIDER_CLIENT_ID"
          ClientSecretEnv: "MY_PROVIDER_CLIENT_SECRET"

This plugin also sets a header with a claim from the Provider, as it has become reasonably common. Claim name and header name can be modified. The default claim is preferred_username, the default header name is X-Forwarded-User:

http:
  middlewares:
    my-provider-openid:
      plugin:
        traefik-oidc-relying-party:
          ProviderURL: "my-provider-url.com" # <- Also supports complete URL, e.g. https://my-provider-url.com/auth
          ClientID: "<CLIENT_ID>"
          ClientSecret: "<CLIENT_SECRET>"
          UserClaimName: "my-uncommon-claim"
          UserHeaderName: "X-Custom-Header"