At a guess, it’s handled (poorly) server side.

There’s this general problem:

My password was too long for Sync and Voyager and now also Boost; I’ve been using Jerboa since it worked in that client.

Since Boost also had the issue I changed my password to a shorter one.

The old one was something like

Friday-Ramble-Patriot-Apricot5-Tractor-Litigator-Shove-Antivirus

… and the new one is shorter and is causing no issues.

Commodore fucking 64

(Undergirded ever so slightly by a Raspberry Pi but don’t mention it)