application_controller.rb

class ApplicationController < ActionController::Base
  # Prevent CSRF attacks by raising an exception.
  # For APIs, you may want to use :null_session instead.
  protect_from_forgery with: :exception
  before_action :set_cookies

  private

  def set_cookies
    if !cookies.permanent[:token]
          cookies.permanent[:token] = {
              value: SecureRandom.random_number,
              domain: "mydomain",
              expires: 1.day.from_now.utc
             }
      end
  end
end

def set_cookies
   unless cookies[:token].present? # Weak naming (token? meaning?) ! + http://apidock.com/rails/ActionDispatch/Cookies/CookieJar/permanent
          cookies.permanent.signed[:token] = {
              value: SecureRandom.random_number,
              domain: "mydomain",
              expires: 1.day.from_now.utc
             }
      end
  end