Add authorization rule for create user by unsigned user

Add authorization to failed user save path cause it was complaining
that no authorization was performed in that path.

app/controllers/proposal_controller.rb

@@ -34,6 +34,7 @@ class ProposalController < ApplicationController
     # If user is not signed in then first create new user and then sign them in
     unless current_user
       @user = User.new(user_params)
+      authorize! :create, @user
       if @user.save
         sign_in(@user)
       else

app/models/ability.rb

@@ -44,7 +44,7 @@ class Ability
 
     # can view Commercials of confirmed Events
     can :show, Commercial, commercialable_type: 'Event', commercialable_id: Event.where(state: 'confirmed').pluck(:id)
-    can :show, User
+    can [:show, :create], User
     unless CONFIG['authentication']['ichain']['enabled']
       can [:show, :create], Registration do |registration|
         registration.new_record?

spec/models/ability_spec.rb

@@ -56,6 +56,7 @@ describe 'User' do
       it{ should_not be_able_to(:show, commercial_event_unconfirmed)}
 
       it{ should be_able_to(:show, User)}
+      it{ should be_able_to(:create, User)}
 
       it{ should be_able_to(:create, Registration)}
       it{ should be_able_to(:show, Registration.new)}