FIX: redirect client to the original url after logging in for private instances

app/controllers/application_controller.rb

@@ -346,6 +346,8 @@ class ApplicationController < ActionController::Base
     def redirect_to_login_if_required
       return if current_user || (request.format.json? && api_key_valid?)
 
+      # save original URL in a cookie
+      cookies[:destination_url] = request.original_url unless request.original_url =~ /uploads/
       redirect_to :login if SiteSetting.login_required?
     end