Only allow a specific web site to show a path via an iframe

Problem/Motivation

It's great that you are able to allow one or more paths to be embedded in another web site via an iframe, simply by adding a simple line, such as /my-shared-article.

However, this page can now be embedded in any web site. It would be awesome if you could also specify a web site, and make it the only one allowed to embed the page. Configuration could be done like this:

/my-shared-article|example.org

Now, example.org is allowed to show /my-shared-article in an iframe on their web site, any other web site are not.

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes