Fix authorization of new and create in ConferenceRegistrationsController

Before authorization we need to set conference relation.
Change in proposal spec cause conference has to have valid registration
period for successful redirect to registration after confirm proposal.

app/controllers/conference_registrations_controller.rb

@@ -1,7 +1,7 @@
 class ConferenceRegistrationsController < ApplicationController
   before_filter :authenticate_user!, except: [:new, :create]
   load_resource :conference, find_by: :short_title
-  authorize_resource :conference_registrations, class: Registration
+  authorize_resource :conference_registrations, class: Registration, except: [:new, :create]
   before_action :set_registration, only: [:edit, :update, :destroy, :show]
 
   def new
@@ -25,8 +25,9 @@ class ConferenceRegistrationsController < ApplicationController
       return
     end
 
-    @registration = Registration.new
-
+    @registration = Registration.new(conference_id: @conference.id)
+    # make sure that conference is open for registration
+    authorize! :new, @registration
     # @user variable needs to be set so that _sign_up_form_embedded works properly
     @user = @registration.build_user
   end
@@ -50,6 +51,7 @@ class ConferenceRegistrationsController < ApplicationController
     end
 
     @registration.user = @user
+    authorize! :create, @registration
 
     if @registration.save
       # Trigger ahoy event