```ruby
# frozen_string_literal: true

require "#{Rails.root}/lib/experiments/fall2017_cmu_experiment"

module Experiments
  class Fall2017CmuExperimentController < ApplicationController
    before_action :set_course_and_check_email_code, only: %i[opt_in opt_out]
    before_action :require_admin_permissions, only: :course_list

    def opt_in
      Fall2017CmuExperiment.new(@course).opt_in
      flash[:notice] = 'Thanks for opting in!'
      redirect_to "/courses/#{@course.slug}"
    end

    def opt_out
      Fall2017CmuExperiment.new(@course).opt_out
      flash[:notice] = 'Okay, you have opted out.'
      redirect_to "/courses/#{@course.slug}"
    end

    def course_list
      send_data Fall2017CmuExperiment.course_list,
                filename: "fall2017-cmu-experiment-courses-#{Time.zone.today}.csv"
    end

    private

    def set_course_and_check_email_code
      @course = Course.find(params[:course_id])
      code = @course.flags[Fall2017CmuExperiment::EMAIL_CODE]
      raise IncorrectEmailCodeError if code.nil?
      raise IncorrectEmailCodeError unless code == params[:email_code]
    end
  end

  class IncorrectEmailCodeError < StandardError; end
end
```

Update opt-in flash message for CMU experiment
user
```ruby
# frozen_string_literal: true

require "#{Rails.root}/lib/experiments/fall2017_cmu_experiment"

module Experiments
  class Fall2017CmuExperimentController < ApplicationController
    before_action :set_course_and_check_email_code, only: %i[opt_in opt_out]
    before_action :require_admin_permissions, only: :course_list

    def opt_in
      Fall2017CmuExperiment.new(@course).opt_in
      flash[:notice] = 'Thank you for opting in. We will add the video sessions to the relevant assignments on the timeline for your WikiEd dashboard and send you an email about next steps.'
      redirect_to "/courses/#{@course.slug}"
    end

    def opt_out
      Fall2017CmuExperiment.new(@course).opt_out
      flash[:notice] = 'Okay, you have opted out.'
      redirect_to "/courses/#{@course.slug}"
    end

    def course_list
      send_data Fall2017CmuExperiment.course_list,
                filename: "fall2017-cmu-experiment-courses-#{Time.zone.today}.csv"
    end

    private

    def set_course_and_check_email_code
      @course = Course.find(params[:course_id])
      code = @course.flags[Fall2017CmuExperiment::EMAIL_CODE]
      raise IncorrectEmailCodeError if code.nil?
      raise IncorrectEmailCodeError unless code == params[:email_code]
    end
  end

  class IncorrectEmailCodeError < StandardError; end
end
```
assistant