Doing this would not be secure in any way - being an HTML file that is hosted on the internet, anyone can gain access with just a single URL. If you would like to sell an HTML game, consider wrapping it in something like NW.js
Couldn't it require log in to an itch.io account that has paid? There are plenty of websites you can't access without logging in.
It is hypothetically possible, bu none the less its insecure.
