An auth_source url could be http:// to any host. Anyone on the path
to a public root, or anyone who can spoof its DNS name, can then
answer hasJoined with a 200 and log in as any player of that source,
including a third-party account linked to staff. The player's IP also
travels in cleartext. Mojang logins are unaffected, since that source
is built in over https.
Config load now refuses http:// unless the host is localhost or a
loopback or private IP address (127.0.0.0/8, ::1, 10/8, 172.16/12,
192.168/16, fc00::/7), so a root on the same host or the LAN still
works without TLS. The decision is made on the literal host because
nothing is resolved at load time, so a LAN root named by hostname
needs its IP address or https. The error says what to change.
The new test covers public names and addresses, link-local, 0.0.0.0
and the first address past 172.16/12 (all refused over http, all
accepted over https), and the loopback and private forms that stay
allowed. It fails on the old check.