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61 lines
2.9 KiB
Markdown
61 lines
2.9 KiB
Markdown
# swarm-authelia-bridge
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The only thing allowed to write `swarm-authelia`'s users database.
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## Why this exists
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`swarm-controller`'s `CreateIdentity` job needs to add an agent as an
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authelia subject, but `swarm-controller` runs unprivileged and does not own
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`users.yml` — a different uid does (`authelia-swarm`, the user
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`services.authelia.instances.swarm` runs as). Root/`CAP_CHOWN`/a shared
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group were all examined and rejected during this crate's design thread —
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see `swarmctl/README.md`'s identical analysis of this same file, written
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before this crate existed.
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The fix: run **this** process as `User = "authelia-swarm";` instead —
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inside the `swarm-authelia` container, alongside authelia itself — so it
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simply owns the file it writes. No elevated privilege anywhere.
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## Shape
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- One endpoint, `POST /requests`, body = `swarm-authelia-bridge-sock`'s
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`BridgeRequest` verbatim — `EnsureAgentIdentity` (idempotently ensure an
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agent exists as an authelia subject) and `ListAgentIdentities` (the
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roster: the subjects carrying the agent marker group, names only).
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- Bearer-authenticated via authelia's own OIDC token introspection (RFC
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7662), against `swarm-controller`'s **existing** machine-client identity
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(already minted for the queue connection) — no new credential.
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- No restart of authelia after a write — relies on
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`authentication_backend.file.watch`, confirmed working against the
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pinned 4.39.20 build during this design work.
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- Network-facing rather than unix-socket-only: `swarm-authelia`'s container
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shares the host netns, so the same listener serves both a co-located
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`swarm-controller` (loopback) and a split-host one (bind wider + firewall)
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with no separate transport.
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## One store, two writers
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This bridge and `swarmctl` both read and write authelia's `users.yml`
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directly. That is the whole arrangement — neither keeps a private copy it
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considers canonical.
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It used to be otherwise, and the seam was real: each side had its own
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`users.json` treated as authoritative, rendering the _same_ physical
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`users.yml`. A writer whose own JSON was missing could not tell "nothing
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here yet" from "someone else's users", so it refused to write at all —
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which is exactly what a hive with existing users hit (#3422).
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What still has to hold, since two processes share the file:
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- **Read before write.** Both do, so neither can drop a user the other
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added between operations.
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- **Unknown keys survive.** Both carry unmodelled top-level and per-user
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fields through a round-trip, or whichever writes second would silently
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delete what the first added.
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- **Every user gets an email.** A relying party asking for the claim fails
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rather than degrades, so both write paths fill in a synthetic address
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when none was supplied.
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Neither restarts authelia: it watches the file. `swarmctl` _could_ (it is
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root); this bridge deliberately cannot, and a reload that depends on which
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process wrote is not a reload.
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