# swarm-authelia-bridge

The only thing allowed to write `swarm-authelia`'s users database.

## Why this exists

`swarm-controller`'s `CreateIdentity` job needs to add an agent as an
authelia subject, but `swarm-controller` runs unprivileged and does not own
`users.yml` — a different uid does (`authelia-swarm`, the user
`services.authelia.instances.swarm` runs as). Root/`CAP_CHOWN`/a shared
group were all examined and rejected during this crate's design thread —
see `swarmctl/README.md`'s identical analysis of this same file, written
before this crate existed.

The fix: run **this** process as `User = "authelia-swarm";` instead —
inside the `swarm-authelia` container, alongside authelia itself — so it
simply owns the file it writes. No elevated privilege anywhere.

## Shape

- One endpoint, `POST /requests`, body = `swarm-authelia-bridge-sock`'s
  `BridgeRequest` verbatim — one variant today (`EnsureAgentIdentity`,
  idempotently ensure an agent exists as an authelia subject).
- Bearer-authenticated via authelia's own OIDC token introspection (RFC
  7662), against `swarm-controller`'s **existing** machine-client identity
  (already minted for the queue connection) — no new credential.
- No restart of authelia after a write — relies on
  `authentication_backend.file.watch`, confirmed working against the
  pinned 4.39.20 build during this design work.
- Network-facing rather than unix-socket-only: `swarm-authelia`'s container
  shares the host netns, so the same listener serves both a co-located
  `swarm-controller` (loopback) and a split-host one (bind wider + firewall)
  with no separate transport.

## Known limitation

`swarmctl` still writes an independent `users.json`/`users.yml` for human
accounts, assuming co-location with `swarm-controller`'s host. Two
canonical stores for the same physical file is a real seam, not solved
here — routing `swarmctl` through this bridge too is a plausible follow-up,
out of scope for the agent-identity slice this crate shipped with.