site_nested_controller.rb

# Loads @site into controller and check if current user is authorized
# to view this site.
module SiteNestedController
  extend ActiveSupport::Concern

  included do
    class_attribute :site_param
    self.site_param = :site_id

    before_action :require_user
    around_action :load_site
  end

  protected def load_site
    @site = Site.find(params[self.class.site_param])
    @site.with_tz do
      if @site.authorizes?(current_user)
        session[:current_site_id] = @site.id
        yield
      else
        access_denied
      end
    end
  end
end