hyperhive/nix/host-modules/glue-matrix-minter-bao-identity.nix
atlas f778122f5a matrix: mint the appservice sender token in the matrix container
A swarm runs one homeserver and a homeserver has one appservice sender
account, so "mint it once" is a property of the thing being minted
rather than something a lock has to enforce. That is what makes this
account the one to move first: no trigger route, no controller change
and no agent list — a boot-time oneshot beside tuwunel is the whole
mechanism.

`swarm-matrix-minter` runs inside `containers.hive-matrix`, which
already holds the appservice token: the rendered registration is bound
in read-only because that is how tuwunel is handed it. What the
container lacked was an identity of its own, so this adds one — a leaf
from the store's CA with a grant of exactly one path, not the hive's
leaf, which reads every secret in the store.

Both ends of the credential ship here. The minter reads the path it
publishes to before it touches the homeserver, and returning on a
non-empty read IS the "only once"; `hive-c0re`'s `ensure_hive_user`
reads the same path, authenticating with the hive name already in
`HYPERHIVE_HIVE_NAME`. The existing mint-then-`M_USER_IN_USE`-login
ladder stays as the fallback for a store that is empty, unconfigured or
unreachable, which is every swarm deployed before this — so nothing
needs backfilling and nothing breaks if the rest of the sequence never
lands.

The credential is not an admin credential, and is not named like one.
It is the access token of the appservice registration's own
`sender_localpart` — `@hive:<server_name>`, an account the homeserver
creates for itself when it loads the registration. The store path is
`swarm/services/matrix/sender-token`, the host path is
`matrix/access-token`, and the homeserver no longer runs an
`admin_execute` promotion for that account at boot. Everything the hive
provisions with it — the Space, the chat room, their hierarchy and join
rules, the invites — rides on being the creator of those rooms at power
level 100, not on homeserver admin; there is no Synapse admin API here
to need, tuwunel has none.

Two operations do need an admin *sender* and therefore stop working:
`hivectl matrix promote-user` and `hivectl matrix reset-password`, both
`!admin …` messages into `#admins:<server>`, plus the password-reset
recovery path that an agent with a lost password file falls back to.
They are swarm-level operations and are left failing loudly rather than
served by an over-privileged token every other call site would also
carry. The sweep's own admin-rights check and self-repair go with them:
an account that is deliberately not an admin has nothing to check.

`ephemeral = false` stays, and hive root can still read the container's
filesystem. Accepted: what this buys is identity separation — no hive
*process* holds or reads the appservice token — not physical isolation.

Refs #4345
2026-09-20 22:07:16 +02:00

40 lines
1.6 KiB
Nix

# Glue: point the matrix container's minter at the bao leaf minted for it.
#
# ONE PAIRING PER FILE — minter ← bao, and nothing else. Deleting this leaves a
# minter that takes operator-provided certificate paths, which is what any
# deployment not minting its own already does.
#
# ⚠️ The minting is NOT here. ./glue-bao-tls.nix holds the CA and signs the
# leaf, because the thing that owns a private key owns issuing from it. What
# belongs here is the pairing: which paths the minter presents.
#
# ⚠️ Gated on the leaf existing, not on the store being enabled — the same rule
# ./glue-secret-publisher-bao-identity.nix states, and it bites harder here: a
# swarm runs ONE homeserver, so the hive hosting it is the one least likely to
# also be the hive hosting the store.
#
# Everything is `mkDefault`. An operator naming their own paths wins.
{
lib,
config,
...
}:
let
hyperhiveCfg = config.services.hyperhive;
deployCfg = hyperhiveCfg.deploy;
baoDeploy = deployCfg.bao;
# Where ./glue-bao-tls.nix puts the leaves, derived from the reader's own path
# rather than repeating that file's directory literal: an operator who moves
# the PKI moves both, and the two cannot drift apart.
haveMintedPki = baoDeploy.clientCertFile != null;
pkiDir = if haveMintedPki then builtins.dirOf baoDeploy.clientCertFile else null;
in
{
config = lib.mkIf (hyperhiveCfg.enable && deployCfg.matrix.enable && haveMintedPki) {
services.hyperhive.deploy.matrix = {
minterBaoClientCertFile = lib.mkDefault "${pkiDir}/matrix-minter.pem";
minterBaoClientKeyFile = lib.mkDefault "${pkiDir}/matrix-minter-key.pem";
};
};
}