controller_auth_example.rb

class FooController < ApplicationController
  before_filter :user_required!
  before_filter :admin_required!, :only => [:secret]
  
  def not_secret
  end
  
  def secret
  end
end

class ApplicationController < ActionController::Base
  def user_required!
    raise Exception.new('must be user') if !current_user
  end
  
  def admin_required!
    raise Exception.new('must be admin') if !current_user.try(:admin?)
  end
  
  def current_user
    return @current_user if defined?(@current_user)
    @current_user = User.find(session[:user_id])
  end
end