Authentication servers are down

Connecting to a paid Realm via the Java 1.19.2 client has been giving an error message on 2022-10-29 for nearly four hours now (possibly longer) from about 18:00 to 23:00 UTC:

Authentication servers are down. Please try again later, sorry!

I'm getting the same error message with both macOS and Windows versions of the client. Connecting to non-Realms multiplayer servers works fine, of course—as does single player. But Realms is a no-go. There's nothing in the "Minecraft game output" window that gives any hints.

The MojangSupport account on Twitter reports there are no issues. [Mojang Status](https://twitter.com/MojangStatus/) also shows now issues. But clearly there are some issues.