Publish IP addresses used for proof fetching

It would be good if the IP addresses used to fetch web identity proofs could be published somewhere, so they can be whitelisted in firewalls.

The issue names no files or tests. Start by locating where web identity proofs are fetched and how their source IP addresses are managed, then determine where those addresses should be published for firewall whitelisting. Done means the relevant fetch IP addresses are published in a stable, discoverable location.

Written by the indexing model from the issue text.