Traefik Forward Auth

A minimal forward authentication service that provides Google oauth based login and authentication for the traefik reverse proxy.

Why?

• Seamlessly overlays any http service with a single endpoint (see: -url-path in Configuration)
• Supports multiple domains/subdomains by dynamically generating redirect_uri's
• Allows authentication to persist across multiple domains (see Cookie Domains)
• Supports extended authentication beyond Google token lifetime (see: -lifetime in Configuration)

Quick Start

See the (examples) directory for example docker compose and traefik configuration files that demonstrates the forward authentication configuration for traefik and passing required configuration values to traefik-forward-auth.

Configuration

The following configuration is supported:

Flag	Type	Description
-client-id	string	*Google Client ID (required)
-client-secret	string	*Google Client Secret (required)
-secret	string	*Secret used for signing (required)
-config	string	Path to config file
-auth-host	string	Central auth login (see below)
-cookie-domains	string	Comma separated list of cookie domains (see below)
-cookie-name	string	Cookie Name (default "_forward_auth")
-cookie-secure	bool	Use secure cookies (default true)
-csrf-cookie-name	string	CSRF Cookie Name (default "_forward_auth_csrf")
-domain	string	Comma separated list of email domains to allow
-whitelist	string	Comma separated list of email addresses to allow
-lifetime	int	Session length in seconds (default 43200)
-url-path	string	Callback URL (default "_oauth")
-prompt	string	Space separated list of OpenID prompt options
-log-level	string	Log level: trace, debug, info, warn, error, fatal, panic (default "warn")
-log-format	string	Log format: text, json, pretty (default "text")

Configuration can also be supplied as environment variables (use upper case and swap -'s for _'s e.g. -client-id becomes CLIENT_ID)

Configuration can also be supplied via a file, you can specify the location with -config flag, the format is flag value one per line, e.g. client-id your-client-id)

OAuth Configuration

Head to https://console.developers.google.com & make sure you've switched to the correct email account.

Create a new project then search for and select "Credentials" in the search bar. Fill out the "OAuth Consent Screen" tab.

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 all the domains you will allow authentication from, appended with the url-path (e.g. https://app.test.com/_oauth)

Usage

The authenticated user is set in the X-Forwarded-User header, to pass this on add this to the authResponseHeaders as shown here.

User Restriction

You can restrict who can login with the following parameters:

• -domain - Use this to limit logins to a specific domain, e.g. test.com only
• -whitelist - Use this to only allow specific users to login e.g. thom@test.com only

Note, if you pass whitelist then only this is checked and domain is effectively ignored.

Cookie Domains

You can supply a comma separated list of cookie domains, if the host of the original request is a subdomain of any given cookie domain, the authentication cookie will set with the given domain.

For example, if cookie domain is test.com and a request comes in on app1.test.com, the cookie will be set for the whole test.com domain. As such, if another request is forwarded for authentication from app2.test.com, the original cookie will be sent and so the request will be allowed without further authentication.

Beware however, if using cookie domains whilst running multiple instances of traefik/traefik-forward-auth for the same domain, the cookies will clash. You can fix this by using the same cookie-secret in both instances, or using a different cookie-name on each.

Operation Modes

Overlay

Overlay is the default operation mode, in this mode the authorisation endpoint is overlayed onto any domain. By default the /_oauth path is used, this can be customised using the -url-path option.

If a request comes in for www.myapp.com/home then the user will be redirected to the google login, following this they will be sent back to www.myapp.com/_oauth, where their token will be validated (this request will not be forwarded to your application). Following successful authoristion, the user will return to their originally requested url of www.myapp.com/home.

As the hostname in the redirect_uri is dynamically generated based on the orignal request, every hostname must be permitted in the Google OAuth console (e.g. www.myappp.com would need to be added in the above example)

Auth Host

This is an optional mode of operation that is useful when dealing with a large number of subdomains, it is activated by using the -auth-host config option (see this example docker-compose.yml).

For example, if you have a few applications: app1.test.com, app2.test.com, appN.test.com, adding every domain to Google's console can become laborious. To utilise an auth host, permit domain level cookies by setting the cookie domain to test.com then set the auth-host to: auth.test.com.

The user flow will then be:

1. Request to app10.test.com/home/page
2. User redirected to Google login
3. After Google login, user is redirected to auth.test.com/_oauth
4. Token, user and CSRF cookie is validated, auth cookie is set to test.com
5. User is redirected to app10.test.com/home/page
6. Request is allowed

With this setup, only auth.test.com must be permitted in the Google console.

Two criteria must be met for an auth-host to be used:

1. Request matches given cookie-domain
2. auth-host is also subdomain of same cookie-domain

Copyright

2018 Thom Seddon

License

MIT