Traefik Configurable Forward Auth

What problem will this feature address?

Sometimes you might want to protect certain applications using an external auth provider.

Describe the solution you'd like

Using traefik-forward-auth, we can add authorization middleware. Multiple providers can be configured.

Add the following components:

• User- or Organisation-based configurable Auth providers
• Add provider configuration as per the traefik-forward-auth docs
• Offer auth providers in Application > Advanced > Security setting.
• Autodeploy a traefik-forward-auth docker service as per the configured provider

Describe alternatives you've considered

This is currently possible by creating a traefik-forward-auth application, and adding a middleware in Traefik File System > dynamic/middlewares.yml, but would be nice if configurable in a form-based solution.

Additional context

I guess this fits in with #274.

Will you send a PR to implement it?

No

Review the Application > Advanced > Security settings and the existing Traefik File System > dynamic/middlewares.yml approach first. Compare the requested provider configuration with the traefik-forward-auth Provider Setup documentation. Done means configurable user- or organisation-based providers, an automatically deployed traefik-forward-auth service, and middleware support for applications.