FEATURE: add site setting allow_new_registrations which can be used to block all new account registrations

app/controllers/invites_controller.rb

@@ -4,6 +4,7 @@ class InvitesController < ApplicationController
   skip_before_filter :redirect_to_login_if_required
 
   before_filter :ensure_logged_in, only: [:destroy, :create, :check_csv_chunk, :upload_csv_chunk]
+  before_filter :ensure_new_registrations_allowed, only: [:show, :redeem_disposable_invite]
 
   def show
     invite = Invite.find_by(invite_key: params[:id])
@@ -137,4 +138,11 @@ class InvitesController < ApplicationController
     params[:email]
   end
 
+  def ensure_new_registrations_allowed
+    unless SiteSetting.allow_new_registrations
+      flash[:error] = I18n.t('login.new_registrations_disabled')
+      render layout: 'no_js'
+      false
+    end
+  end
 end