Restrict ethercalc service to selected domain.

Hi, thanks for this amazing software.
I would like to enquire about a problem.
I have a service running on port 8000 using https. It is accessible to everyone, but I want to restrict this to selected domains. 
I am using this service and iframe, but I want to add the check that if referer is not from those domains, don't display any data.

I have tried to modify main.js but I gets errors.