This would be used as a route constraint in the routes.rb file, so I wouldn't be able to call `redirect_to` from here.

If the user is unauthorized, I `throw(:warden)` to let warden then delegate to the failure app. The warden failure app can then figure out where to redirect to (either 401, or redirect to the sign_in_path).

If this method returns `false`, then the Rails responds with 404 Not Found because the route constraint is not satisfied, instead of 401 indicating that the route exists but the user doesn't have permission to access it.