What why?
Why ask here?
If you want to pull and store more data from Itch.io than what is already stored by the browser, then it looks like you’re doing something beyond making a nicer UI. Is it not something to collaborate with the Itch.io team on— assuming it’s not malicious like existing labeling extensions i’ve seen that aren’t site specific?
Maybe I didn't explain my use case clearly.
Yes, I can extract all the metadata I need from the game page itself. The problem is that I want to display that information on my extension's settings page, which is separate from itch.io.
That means I either have to cache all of the game's metadata locally (which significantly increases the amount of stored data and requires a mechanism to keep it up to date), or store only an identifier and fetch the rest when needed.
I think the second approach is preferable. In fact, I can already do it using URLs like https://username.itch.io/game-slug/data.json. What I don't like is that this requires storing the author's username and the game's slug instead of a single immutable ID.
Besides taking up more space, usernames and slugs can change over time, while the game's ID remains constant.