feature: auto-redirect to IDP when only one exists

[clintharrison]

I'm using caddy-security with a single authn backend.

Instead of presenting a login page with a single button, it'd be great if /login redirected there immediately, since that's what the user will do anyway.

I suppose we could add a Caddyfile directive so this is opt-in behavior :)

[greenpau]

@clintharrison , have you looked into adding custom javascript to do the automatic redirect? https://authp.github.io/docs/authenticate/ui-features#javascript

[greenpau]

This feature does make sense. Will add it next time I do the refactoring of UI