stac info /path/to/catalog.jsonseems like a natural utility to add to that. Are you going to be at the STAC sprint, and want to touch base around potentially combining efforts on that?
sentinel-s2-l2a-cogscollection is what you want.
sentinel-s2-l2aare catalogs for the original JP2K files in eu-central-1 and are in requester pays buckets. But the COGs are free