authelia 4.39.20 exits at startup on `users: {}` ("users: non zero value
required"), and the first-boot unit seeded exactly that, so a swarm with
no users crash-looped authelia and answered 502 until `swarmctl user add`
ran.
The first-boot unit now writes one subject, `swarm.placeholder`, when
the users database is absent, empty, or exactly `users: {}`:
- `disabled: true` — authelia returns "user not found" for a disabled
user before any password check (file_user_provider.go,
CheckUserPassword).
- password: an argon2id digest with an all-zero key. It decodes (authelia
rejects a non-digest at startup) and no known password hashes to it.
- the `.` keeps it out of agent names (`[a-z0-9-]`), and `swarmctl user
add` refuses it as already existing. Neither writer removes users, and
both round-trip `disabled`.
A file with any user in it is never touched.
The docs that described the crash-loop (sso.md, gateway.md, setup.md,
the sso-unavailable error page) now describe the placeholder; the
writers' load_store docs and the seed fixtures follow. module-eval
nats-authelia asserts the seed branch.