I needed a simple app icon solution for RevenueCat, was surprised it didn't exist. So I built it.
It's a node server that uses the iTunes Search API to fetch the URL for the app icon, caches the URL, then redirects the request to Apple's CDN.
Would it be possible to add a search or lookup of some kind? Needing to know the Bundle ID makes this a bit tricky to use for anything but your own apps.