Rails：在CanCan访问被拒绝之前询问用户身份验证

我想显示登录表单而不是cancan访问被拒绝的Flash消息。这是我的控制器

#app/controllers/oferts_controller.rb
class OfertsController < ApplicationController
  before_action :set_ofert, only: [:show, :edit, :update, :destroy]
  load_and_authorize_resource :only => [:new, :edit, :destroy] 
  before_filter :authenticate_user!, :except => [:show, :index]
  # GET /oferts
  # GET /oferts.json
  def index
    @oferts = Ofert.areactive
  end

  # GET /oferts/1
  # GET /oferts/1.json
  def show
  end

  # GET /oferts/new
  def new
    @ofert = current_user.oferts.new
    @ofert.purchasing_group = PurchasingGroup.new
  end

  # GET /oferts/1/edit
  def edit
  end

  # POST /oferts
  # POST /oferts.json
  def create
    ....
  end

  # PATCH/PUT /oferts/1
  # PATCH/PUT /oferts/1.json
  def update
  ....
  end

  # DELETE /oferts/1
  # DELETE /oferts/1.json
  def destroy
   ...
  end

  private
    # Use callbacks to share common setup or constraints between actions.
    def set_ofert
      @ofert = Ofert.find(params[:id])
    end

    # Never trust parameters from the scary internet, only allow the white list through.
    def ofert_params

      params.require(:ofert).permit(:title, :short_title, :description, :price, :normal_price, :ends_at, :ends_at_date, :ends_at_time)
    end
end

由于某些原因，当我尝试访问需要登录的操作（例如“创建”）时，我仅从CanCan收到拒绝访问消息，但由于我具有：authenticate_user，因此我没有按原样重定向到登录页面！控制器中的before_filter。

如何确定设备重定向到登录页面的优先级，而不是优先访问cancan拒绝的Flash消息？

谢谢

更新：这是我的Gemfile

    source 'https://rubygems.org'


# Bundle edge Rails instead: gem 'rails', github: 'rails/rails'
gem 'rails', '4.1.9'
# Use mysql as the database for Active Record
gem 'mysql2'
# Use SCSS for stylesheets
gem 'sass-rails', '~> 5.0.0'
# Use Uglifier as compressor for JavaScript assets
gem 'uglifier', '>= 1.3.0'
# Use CoffeeScript for .js.coffee assets and views
gem 'coffee-rails', '~> 4.0.0'
# See https://github.com/sstephenson/execjs#readme for more supported runtimes
# gem 'therubyracer',  platforms: :ruby

# Use jquery as the JavaScript library
gem 'jquery-rails'
# Turbolinks makes following links in your web application faster. Read more: https://github.com/rails/turbolinks
gem 'turbolinks'
# Build JSON APIs with ease. Read more: https://github.com/rails/jbuilder
gem 'jbuilder', '~> 2.0'
# bundle exec rake doc:rails generates the API under doc/api.
gem 'sdoc', '~> 0.4.0',          group: :doc

gem 'money-rails', '~> 1.2.0'

gem 'money', '~> 6.5.0'
# Use ActiveModel has_secure_password
gem 'bcrypt', '~> 3.1.7'

gem 'foundation-rails'
gem 'font-awesome-rails', '~>4.3.0.0'
gem 'devise'
gem "cancan"
gem "rolify"
gem "paperclip", "~> 4.2"
gem 'rails-i18n', '~> 4.0.0'
gem 'jquery-ui-rails'
gem 'whenever', :require => false
gem 'jquery-countdown-rails'
# Use unicorn as the app server
# gem 'unicorn'

# Use Capistrano for deployment
# gem 'capistrano-rails', group: :development

# Use debugger
# gem 'debugger', group: [:development, :test]

group :development do
    # Spring speeds up development by keeping your application running in the background. Read more: https://github.com/rails/spring
    gem 'spring'
    gem 'quiet_assets', '~>1.1'
end

group :development, :test do
  gem 'rspec-rails', '~> 3.0.0'
  gem 'rspec-expectations'
  gem 'factory_girl_rails', '~> 4.0'
end

group :test do
  gem 'capybara', '~> 2.3.0'
  gem 'capybara-email'
  gem 'shoulda-matchers', '~> 2.7.0'
  gem 'rspec-its'
  gem 'rspec-activemodel-mocks', '~> 1.0.1'
end