Check authentication on each request (#26)

Reviewed-on: #26

app/controllers/application_controller.rb

@@ -1,2 +1,3 @@
 class ApplicationController < ActionController::Base
+  include Authenticatable
 end

app/controllers/concerns/authenticatable.rb

@@ -0,0 +1,13 @@
+module Authenticatable
+  extend ActiveSupport::Concern
+
+  included do
+    before_action :authenticate_user
+  end
+
+  private
+
+  def authenticate_user
+    Current.user = User.find_by(id: session[:current_user_id]) || GuestUser.new
+  end
+end