Hello @Harlequin
I don’t know the answer to the question in your Subject line, but the following post contains clone links to an example app (Luke Skywalker) that allows embedding but supports varied responses to different embedding sites (with additional clone app examples for Ben Kenobi, Darth Vader, and “all other” websites.)
Unfortunately, to get the HTTPS and domain this approach uses a Javascript function that is not presently supported on either desktop Firefox or Android Firefox…