hyperhive/docs/swarm/sso.md

# Swarm SSO

The swarm runs one authelia, and it's two things at once: the **session
provider** every protected vhost checks (`auth_request`), and — once any
client is declared — an **OIDC provider** issuing tokens to relying
parties: the forge and the matrix homeserver.

The second role derives rather than switches:
`services.hyperhive.swarm.authelia.oidc.clients` being non-empty turns it
on. authelia refuses to start with a provider that has no clients, so a
separate `enable` would be a second fact free to disagree with the first.

## Getting in the first time

authelia binds loopback only. The **gateway** on the host running it
publishes it as `auth.<swarm.domain>` — vhost, dnsmasq record and TLS
name all follow `deploy.authelia`, so there is nothing to turn on
separately. (Details, including why a client hive must not declare that
vhost: [`../networking/gateway.md`](../networking/gateway.md).)

**Authelia doesn't start until at least one user exists.** This module
generates the user store empty — deliberately, since seeding a default
account would put a credential in a config file — but authelia validates
it at startup and treats "no users" as fatal:

```
error reading the authentication database: could not validate the schema:
  users: non zero value required
```

It then exits 1 and systemd restarts it, so a swarm that has been
enabled but not bootstrapped shows a **crash-looping unit** and `502 Bad
Gateway` from the vhost — not a login page with nobody able to use it.
The gateway is working in that state; the upstream isn't up.

⚠️ The step below is **required to finish the install**, not an
optional first-login convenience. Run it before concluding anything is
wrong with the proxy: a 502 here means "no users yet" far more often
than it means a routing fault.

Add the first subject on the host running authelia:

```console
# swarmctl user add mara --display-name Mara --email mara@example.com --group admins
added mara to /var/lib/authelia-swarm/users.yml
password: <generated>
this password is stored nowhere — record it now
```

`swarmctl` generates, hashes, and prints the password once, keeping only
the hash. It reads and writes authelia's `users.yml` directly — it's
the one user store, shared with `swarm-authelia-bridge`, which creates
agent identities in the same file. No restart: authelia watches it. Full
reference: [`../tools/swarmctl-cli.md`](../tools/swarmctl-cli.md).

You can edit `users.yml` by hand, and `swarmctl` will read what you
wrote. ⚠️ It rewrites the whole file on every change, so **comments and
formatting don't survive**; values and unrecognised keys do.

This step stays manual on purpose. Bootstrapping an identity provider
non-interactively means a secret arriving from somewhere — a file, an
env var, a nix expression — and every one of those is worse than an
operator typing one command once.

### Changing a subject afterwards

`user add` only ever adds: on a name that already exists it refuses,
rather than resurfacing as a second account or a silent overwrite.
Editing an existing subject is `user update`, and the flags compose, so
one call can change multiple things:

```console
# swarmctl user update mara --add-group admins --email mara@example.com
added to group "admins"
email: unset -> "mara@example.com"
mara is now in groups: admins
```

Two behaviours worth knowing before you rely on them:

- **`--remove-group` fails if the user isn't in that group.** Every
  other flag is idempotent — setting what's already set is fine, so a
  "make these four things true" call doesn't break when one of them
  already was. Revocation is the exception on purpose: a typo'd group
  name that reported success would leave an account holding access you
  believe you took away, and that's the one outcome nobody re-checks.
- **`swarmctl` prints the resulting group list** because group names have no
  registry anywhere. A misspelled `--add-group` creates a real group that
  no access-control rule mentions, so the user gains nothing and no error
  is possible — reading the line back is the only check there is.

Passwords are deliberately out of scope here: regenerating a credential
is a different intent from editing an attribute, and folding them means
an attribute edit can invalidate a login by accident.

## What secrets exist, and where each one lives

Every secret in the swarm, with its generator and its path, is tabulated
in one place: [`secrets.md`](secrets.md), including authelia's own keys
(session, JWT, storage-encryption, OIDC HMAC, OIDC issuer) and the two
halves of each client secret. That page's two rules — a secret is always
a path, never a value, and the generator and the reader typically live in
different containers — are why the client secret's plaintext half needs
the delivery step below and the rest of authelia's keys don't.

## Getting the plaintext to the relying party

Three cases, and they're genuinely different mechanisms rather than one
mechanism with flags.

### 1. All-local — one host runs both

Nothing to configure at all. Per service, a host-side unit waits for
authelia's first boot to mint that client's secret and copies it into the
service's container, and the service's own module contributes its client
entry — callback URL included — to authelia's client list.

The callback is built once and read twice, so the redirect URI authelia
accepts and the one the service actually sends can't drift apart. A
mismatch there is a rejected login with no error text worth reading.

⚠️ The delivery is a copy, not a `bindMounts` entry, and deliberately so:
nixos-container refuses to start a container whose bind source is
missing, and this secret doesn't exist until authelia's first boot has
run. Binding it would make the service wait on a file that waits on a
container that starts after it — on a fresh hive, a permanent stall
presenting as "the forge is broken," many layers from its cause.

### 2. Swarm-managed services

The controller side owns provisioning: `swarmctl` writes both halves, the
same way it already owns authelia's user store (`users.yml`, read and
written in place).

### 3. A hive elsewhere

No shared host, so no automatic path. The operator provides the file and
names it:

```nix
services.hyperhive.swarm = {
  authelia.url = "https://auth.example.com";
  forge.sso = {
    enable = true;
    clientSecretFile = "/var/lib/hyperhive/forge-oidc-secret";
  };
};
```

**This module asserts both at eval.** A hive that boots with SSO
half-configured shows a login button that always fails — a symptom
many layers from its cause, and far worse to diagnose than an
evaluation error.

## Where each relying party differs

The registration half is identical; what each service does with the
result isn't.

|                           | forge                                                                              | matrix                                                                                                           |
| ------------------------- | ---------------------------------------------------------------------------------- | ---------------------------------------------------------------------------------------------------------------- |
| how it learns the config  | a oneshot calls `forgejo admin auth`, writing a login-source row into its database | tuwunel reads a `[[global.identity_provider]]` entry from its config file                                        |
| how it reads the secret   | a path inside its container                                                        | the same path, handed on by `LoadCredential`                                                                     |
| callback URL              | `<root>/user/oauth2/<source>/callback`                                             | `<homeserver>/_matrix/client/unstable/login/sso/callback/<client_id>`, a shape tuwunel fixes rather than accepts |
| cost of a malformed entry | the login source is missing                                                        | the homeserver can refuse to start                                                                               |

Two consequences worth stating plainly:

- **tuwunel re-reads its secret file on every OAuth exchange**, not only
  at startup, and its own sandboxing hides most paths from it. It gets the
  file through `LoadCredential` for the same reason the registration token
  does — that keeps `DynamicUser` and `PrivateUsers` intact, with no
  host-side ownership arrangement to maintain.
- **Matrix SSO lives inside the homeserver.** The client-server API is
  spoken by non-browser clients holding matrix access tokens — every
  agent's own daemon — as well as by federation, so the homeserver
  serves `/_matrix/` directly and authenticates it itself. The
  forward-auth vhosts protect browser surfaces; this isn't one of them.

## Machine clients

Everything above is a person in a browser. A swarm also has callers that
hold no session and follow no redirect: the telemetry collector, the
queue's auth-callout responder, and each hive's own agents.

**One client per hive, not one per service.** A hive's identity belongs to
the directory rather than to whichever service happens to consume it, so a
hive holds a single OIDC client — `<hiveClientPrefix><hive>` — and mints a
different token per service from it. The alternative, letting each
consuming subsystem declare its own list, collides on the same client id
the moment a second consumer appears.

**The audience is that client id.** A swarm service that has to tell hives
apart needs one name both sides already agree on, and the client id is
already that name. A parallel per-hive naming scheme would be a second
thing to keep in step, and it drifts silently — a mismatch presents as a
valid token refused at the target, which reads like a broken credential
rather than a broken name.

**Authelia signs tokens (`RS256`), not opaque ones**, because a resource server
that can't call the provider back is a real case here: the telemetry
collector verifies offline against `/jwks.json`, and an opaque token gives
it nothing to verify. The queue's responder introspects instead — a
different question asked of the same token, and the reason both
`/api/oidc/introspection` and `/jwks.json` have to stay reachable.

### Machine callers must fail closed

⚠️ **An error page that answers `200` is a security bug, not a cosmetic
one.** The browser surface intercepts upstream errors and serves a
friendly "SSO is unavailable" page; that page is a file, so it returns
`200`. Any machine caller routed through it receives a success carrying
HTML instead of the failure that actually happened:

- `/api/authz/auth-request` — nginx `auth_request` treats **any 2xx as
  success**, so a down provider means _access granted_
- `/api/oidc/introspection` — a token check that answers `200`
- `/api/oidc/token`, `/.well-known/openid-configuration` — a client
  parsing an error page as its JSON document

The gateway routes authelia's `/api/` and `/.well-known/` prefixes
**without** error interception. The split is by _audience_, not by an enumerated path
list: a human gets the page, every machine caller gets the status.
Enumerating endpoints individually would leave the next one added
silently intercepted.

The same shape bites any machine route behind a browser-shaped gate: the
caller follows a `302` to a login page, the login page answers `200`,
and the caller reports success while nothing happened. Log ingest hit exactly this
and lost eleven hours of delivery in silence.

**Checking it, if you change this routing.** Point the vhost at a dead
upstream and compare three requests, not one:

1. through `/` — must still serve the friendly page
2. through `/api/` — must deny
3. a direct dial to authelia — must match what (2) did

All three matter. A change that silently deleted the browser page would
pass a deny-only check, and one that quietly stopped denying would pass a
page-only check. This was verified that way when the split was introduced.

## What this doesn't do

- **It doesn't disable local login.** Each service keeps its password
  database and gains a second door. An identity provider that can take a
  service offline when it hiccups is worse than one with two ways in.
  Making authelia the only path is a separate, reversible switch per
  service (tuwunel's `login_with_password`, forgejo's own setting).
- **It doesn't provision users.** Agents are created and destroyed
  continuously, so the subject set belongs to a program rather than to a
  config file; today that program is `swarmctl`.