Rlogin

Rlogin (RFC 1282-ish — see below) gives single-sign-on terminal
access. Port 513/tcp. Mostly used by inter-BBS game servers
where one BBS launches a game on another and the player travels with
their identity intact.

Off by default. Rlogin is unauthenticated and unencrypted — a
client's claimed username is trusted at face value — so
RLOGIN_ENABLED defaults to false. A sysop has to explicitly turn
it on (and should only do so on a trusted network, or firewalled to
known peers) before this port answers at all.

How it works

The client opens a connection to port 513 and sends three null-
terminated strings:

\0 client-username \0 server-username \0 terminal/baud \0

The server reads them, validates against its allowlist, and drops the
user straight into the menu (or directly into a door if the rlogin
was for a specific game).

Synchronet game-server caveat

Synchronet-flavored rlogin uses an inverted field order vs the
standard:

password first, username second.

ANetBBS's outbound door_rlogin game type follows the Synchronet
convention. See rlogin doors
for the details on the remote-game flow.

Locally

Note the current Web Terminal does not go through rlogin — it
opens a plain socket straight to the local Telnet listener, so
you still see the normal login prompt inside the browser terminal.
Rlogin's local auto-login handshake (username pre-filled, no
password re-prompt) is for genuine rlogin clients — other BBS
software launching a door on this system, or a sysop's own rlogin
client — not the web UI.