Share cameras or some HA entities by QR code with friends with another HA

Very often there are situations when several cameras are installed at the entrance by different people. It would be great if HA owners could easily share camera access via QR code. Also, sometimes someone puts a temperature sensor outdoor, it would be great so that these readings could be shared with a friend. I know that this requires a domain with HA or Nabu Casa. You also need an admin panel for such access, so that you can revoke access at any time. Also, this will sometimes work when two users are connected to the same provider even without an external IP address, since sometimes the provider will allow two computers to be connected to each other using a gray IP address.