asciinema.org/app/controllers/application_controller.rb

class NotFound < StandardError; end

class ApplicationController < ActionController::Base
  protect_from_forgery

  class Unauthorized < Exception; end
  class Forbidden < Exception; end

  rescue_from ActiveRecord::RecordNotFound, :with => :not_found
  rescue_from Unauthorized, :with => :unauthorized
  rescue_from Forbidden, :with => :forbidden

  helper_method :current_user

  def current_user
    if permanent_store[:auth_token]
      @current_user ||= find_user_by_auth_token(permanent_store[:auth_token])
    end
  end

  def current_user=(user)
    if user
      permanent_store.permanent[:auth_token] = user.auth_token
    else
      permanent_store.delete(:auth_token)
    end
  end

  private

  def permanent_store
    cookies
  end

  def find_user_by_auth_token(auth_token)
    user = User.where(auth_token: auth_token).first
    user && user.decorate
  end

  def ensure_authenticated!
    raise Unauthorized unless current_user
  end

  def omniauth_credentials
    OmniAuthCredentials.new(request.env['omniauth.auth'])
  end

  def store_location
    session[:return_to] = request.path
  end

  def get_stored_location
    session.delete(:return_to)
  end

  def redirect_back_or_to(default, options = nil)
    path = get_stored_location || default

    if options
      redirect_to path, options
    else
      redirect_to path
    end
  end

  def forbidden
    if request.xhr?
      render :json => "Forbidden", :status => 403
    else
      redirect_to root_path, :alert => "This action is forbidden"
    end
  end

  def unauthorized
    if request.xhr?
      render :json => "Unauthorized", :status => 401
    else
      store_location
      redirect_to login_path, :notice => "Please sign in to proceed"
    end
  end

  def not_found
    respond_to do |format|
      format.any do
        render :text => 'Requested resource not found', :status => 404
      end

      format.html do
        render 'application/not_found', :status => 404, :layout => 'application'
      end
    end
  end
end