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swarm-nats-auth: verify an agent's own token against the store

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An `auth_token` spelled `swarm-agent.<agent>.<secret>` is no longer sent
to introspection. The responder reads `swarm/agents/<agent>/queue` with
an identity of its own, checks that the stored object names the same
agent, compares the secret in constant time, and grants the subjects
`--agent-token-publish-subject` lists with `{agent}` expanded. Every
other outcome denies: a malformed token, no store identity, nothing
stored, a failed or slow lookup, a different secret. A token without
the prefix takes the OIDC path unchanged.

The journal's `auth request` line names such a caller `agent:<agent>`;
the hive-shared credential keeps `hive-<h>-agent`.

The new principal: a `swarm-nats-auth` cert-auth role and policy with
read on `secret/data/swarm/agents/+/queue` alone, a leaf signed by the
store's PKI glue, and `glue-nats-auth-bao-identity.nix` pairing the two.
The copy unit delivers the identity into the queue's container, and an
absent leaf is delivered empty so the responder still starts and only
agent tokens are refused.

The policy and role are written by `swarm-bao-nats-auth-policy`, logged in
as the bao granter: both names fall under its `swarm-*` globs, so the
deploy writes them with no operator step. module-eval counts it among the
granting units, so every generic granting-unit case covers it.

The secret compare uses `subtle`, already in the lock file through the
TLS stack; no workspace crate offered one directly.
This commit is contained in:
atlas 2026-09-27 20:38:34 +02:00
commit 9bad58d86d
14 changed files with 846 additions and 51 deletions
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44
nix/module-eval/bao-grants.nix
View file

@ -151,7 +151,7 @@ let
_: u: (u.environment.BAO_CLIENT_CERT or null) == granterCertFile
) baoGrantWithConsumers.systemd.services;
# The eleven units that write a `swarm-*` grant, by name, for the discovery
# The twelve units that write a `swarm-*` grant, by name, for the discovery
# control below.
grantingUnitNames = [
"swarm-bao-controller-policy"
@ -165,6 +165,7 @@ let
"swarm-bao-services-issuer-policy"
"swarm-bao-nats-tls-policy"
"swarm-bao-agent-pki"
"swarm-bao-nats-auth-policy"
];
# Comment lines dropped first: both the HCL and the scripts explain
@ -561,6 +562,33 @@ let
&& !(lib.hasInfix "swarm-grafana" s)
&& !(lib.hasInfix "sys/policies/acl" s);
}
{
# `+` is one path segment, so this reaches `swarm/agents/<agent>/queue`
# and no other credential an agent holds; `swarm/agents/*` would reach
# all of them.
name = "the queue responder's grant is every agent's queue credential and nothing else";
ok =
let
s = baoGrantHere.systemd.services.swarm-bao-nats-auth-policy.script;
in
lib.hasInfix "path \"secret/data/swarm/agents/+/queue\" {" s
&& lib.hasInfix "capabilities = [\"read\"]" s
&& lib.length (lib.filter lib.isList (builtins.split "path \"" s)) == 1
&& !(lib.hasInfix "secret/data/swarm/agents/*" s)
&& !(lib.hasInfix "secret/data/swarm/hives" s)
&& !(lib.hasInfix "secret/data/swarm/services" s)
&& lib.hasInfix "auth/cert/certs/swarm-nats-auth" s
&& lib.hasInfix "allowed_common_names=swarm-nats-auth" s
&& lib.hasInfix "token_policies=swarm-nats-auth" s;
}
{
name = "the PKI unit signs the queue responder's leaf under its own subject";
ok =
let
s = baoGrantHere.systemd.services.swarm-bao-pki.script;
in
lib.hasInfix "/nats-auth.pem ]" s && lib.hasInfix "swarm-nats-auth \"\" clientAuth" s;
}
{
# 🩸 The half that makes the policies above bind: a policy grants only
# through a token that carries it, and a token is minted by a cert-auth
@ -748,24 +776,24 @@ let
}
{
# A store host without the granter's pair writes its grants some other
# way, so none of the eleven units may exist. Without this arm
# way, so none of the twelve units may exist. Without this arm
# `lib.mkIf haveGranter` could be dropped from any of them and every other
# case here would still pass.
name = "without the granter's pair none of the eleven granting units render";
name = "without the granter's pair none of the twelve granting units render";
ok =
let
s = baoGranterOptOut.systemd.services;
in
lib.all (unit: !(s ? ${unit})) (grantingUnitNames ++ [ "swarm-bao-granter-role" ])
# The control: the same store with the pair renders all eleven.
# The control: the same store with the pair renders all twelve.
&& lib.all (unit: baoGrantHere.systemd.services ? ${unit}) grantingUnitNames;
}
{
# 🩸 What replaced the silent skip. With no bootstrap token the eleven still
# 🩸 What replaced the silent skip. With no bootstrap token the twelve still
# render, and a refused granter fails them with the step that fixes it.
# A store host that never named a token is told to name one, since the
# unit that sets the granter up renders only where it has.
name = "a store host without a bootstrap token renders the eleven, each failing loudly with the one-time step";
name = "a store host without a bootstrap token renders the twelve, each failing loudly with the one-time step";
ok =
let
s = baoGranterNoToken.systemd.services;
@ -1129,8 +1157,8 @@ let
}
{
# What makes the case above mean something: discovery by the granter's
# certificate reaches all eleven units, and each yields calls.
name = "the granter-policy check sees all eleven granting units, and parses calls from each";
# certificate reaches all twelve units, and each yields calls.
name = "the granter-policy check sees all twelve granting units, and parses calls from each";
ok =
lib.sort lib.lessThan (lib.attrNames granterUnits) == lib.sort lib.lessThan grantingUnitNames
&& lib.all (u: baoCalls u.script != [ ]) (lib.attrValues granterUnits)