swarm-bao: grant the queue responder the callout issuer and user keys' leaves

The `swarm-nats-auth` policy grants create and read, never update, on the
seed and public half of the callout issuer and user keys, beside the xkey's
two leaves: `ensure-callout-keys` creates them under that role, and the
responder reads both seeds as it starts.

The `swarm-secret-publisher` policy, which may write the rest of
`swarm/services/`, is denied both seed paths exactly, as it is the xkey's.
A planted issuer seed would be the authority to admit anyone to the queue.

Both policies are written by the granter on every deploy; nothing about the
granter's own policy changes.

nix/host-modules/swarm-bao.nix

@@ -469,9 +469,11 @@ let
   # Write-only. It copies secrets in and never reads one back; a read
   # capability would let a file-copier recover every hive's credentials.
   #
-  # The callout xkey's seed sits under `swarm/services/` and is no secret this
+  # The queue callout's three seeds sit under `swarm/services/` and are no
-  # principal copies, so its exact path, which outranks the prefix, is denied:
+  # secret this principal copies, so their exact paths, which outrank the
-  # a write there would replace the key every queue request is sealed to.
+  # prefix, are denied. A write to the xkey's would replace the key every
+  # queue request is sealed to; the issuer's is the authority to admit anyone
+  # to the queue, and the user's is the one identity exempt from callout.
   secretPublisherPolicyText = ''
     path "${credentialMountPath}/data/swarm/hives/*" {
       capabilities = ["create", "update"]
@@ -485,6 +487,14 @@ let
       capabilities = ["deny"]
     }
 
+    path "${credentialMountPath}/data/${issuerSeedLeaf}" {
+      capabilities = ["deny"]
+    }
+
+    path "${credentialMountPath}/data/${userSeedLeaf}" {
+      capabilities = ["deny"]
+    }
+
     path "${credentialMountPath}/data/${controllerClientLeaf}" {
       capabilities = ["create", "update"]
     }
@@ -858,10 +868,10 @@ let
   # other credential an agent holds. Plus the responder's own OIDC client
   # secret, which `swarm-bao-nats-auth-oidc` reads under this same leaf.
   #
-  # And the callout xkey's two leaves, which `ensure-xkey` creates when the
+  # And the two leaves of each callout key, which `ensure-callout-keys`
-  # store holds no seed. `create` without `update`, so a stored pair is never
+  # creates when the store holds no seed. `create` without `update`, so a
-  # replaced; `read` because creating is read-then-create, and the responder
+  # stored pair is never replaced; `read` because creating is
-  # loads the seed as it starts.
+  # read-then-create, and the responder loads the seeds as it starts.
   natsAuthReaders = [
     {
       name = "swarm-nats-auth";
@@ -869,17 +879,28 @@ let
       policyText =
         readStanza "${credentialMountPath}/data/swarm/agents/+/queue"
         + readStanza "${credentialMountPath}/data/swarm/services/${hyperhiveCfg.swarm.nats.clientId}/oidc/client"
-        + createStanza "${credentialMountPath}/data/${xkeySeedLeaf}"
+        + lib.concatMapStrings (leaf: createStanza "${credentialMountPath}/data/${leaf}") [
-        + createStanza "${credentialMountPath}/data/${xkeyPublicLeaf}";
+          xkeySeedLeaf
+          xkeyPublicLeaf
+          issuerSeedLeaf
+          issuerPublicLeaf
+          userSeedLeaf
+          userPublicLeaf
+        ];
     }
   ];
 
-  # The callout xkey, the nix half of `swarm-nats-auth`'s `xkey::SEED_PATH`
+  # The callout's keys, the nix half of `swarm-nats-auth`'s `xkey::SEED_PATH`
-  # and `xkey::PUBLIC_PATH`. Both are readable by the `swarm-nats-auth` role
+  # and `xkey::PUBLIC_PATH`, and of the `seed_path` and `public_path` of
-  # alone: `swarm/public/` marks the half that is no secret, and no policy
+  # `nkey::ISSUER` and `nkey::USER`. All are readable by the `swarm-nats-auth`
-  # opens it to every token.
+  # role alone: `swarm/public/` marks the halves that are no secret, and no
+  # policy opens them to every token.
   xkeySeedLeaf = "swarm/services/swarm-nats/callout/xkey-seed";
   xkeyPublicLeaf = "swarm/public/swarm-nats/callout-xkey";
+  issuerSeedLeaf = "swarm/services/swarm-nats/callout/issuer-seed";
+  issuerPublicLeaf = "swarm/public/swarm-nats/callout-issuer";
+  userSeedLeaf = "swarm/services/swarm-nats/callout/user-seed";
+  userPublicLeaf = "swarm/public/swarm-nats/callout-user";
 
   createStanza = path: ''
     path "${path}" {

nix/module-eval/bao-grants.nix

@@ -442,6 +442,24 @@ let
             "update"
           ];
     }
+    {
+      # The same denial for the callout's two nkey seeds: a planted issuer
+      # seed admits anyone to the queue, and a planted user seed is the one
+      # identity callout does not check. Each is its own exact path, so the
+      # OIDC leaf beside them is still the prefix's.
+      name = "the publisher may not write the callout issuer or user seed";
+      ok =
+        let
+          grants = grantsIn baoGrantHere.systemd.services.swarm-bao-secret-publisher-policy.script;
+        in
+        (grantFor grants "secret/data/swarm/services/swarm-nats/callout/issuer-seed").caps == [ "deny" ]
+        && (grantFor grants "secret/data/swarm/services/swarm-nats/callout/user-seed").caps == [ "deny" ]
+        &&
+          (grantFor grants "secret/data/swarm/services/swarm-nats/oidc/client").caps == [
+            "create"
+            "update"
+          ];
+    }
     {
       # The ordering is load-bearing and invisible at runtime: the controller's
       # unit creates the KV and cert-auth mounts this one writes into, so
@@ -590,9 +608,9 @@ let
       # `+` 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. The responder's own OIDC client secret is the one
-      # `services/` leaf beside it. Its only creates are the callout xkey's
+      # `services/` leaf beside it. Its only creates are the two leaves of
-      # two leaves, and nothing it holds may update or delete one.
+      # each callout key, and nothing it holds may update or delete one.
-      name = "the queue responder reads agent queue credentials and its OIDC secret, and may create only the callout xkey's two leaves";
+      name = "the queue responder reads agent queue credentials and its OIDC secret, and may create only the callout keys' leaves";
       ok =
         let
           s = baoGrantHere.systemd.services.swarm-bao-nats-auth-policy.script;
@@ -604,7 +622,11 @@ let
         && lib.length (lib.filter lib.isList (builtins.split "capabilities = \\[\"read\"]" s)) == 2
         &&
           lib.sort lib.lessThan creates == [
+            "secret/data/swarm/public/swarm-nats/callout-issuer"
+            "secret/data/swarm/public/swarm-nats/callout-user"
             "secret/data/swarm/public/swarm-nats/callout-xkey"
+            "secret/data/swarm/services/swarm-nats/callout/issuer-seed"
+            "secret/data/swarm/services/swarm-nats/callout/user-seed"
             "secret/data/swarm/services/swarm-nats/callout/xkey-seed"
           ]
         && lib.all (
@@ -616,7 +638,7 @@ let
               "read"
             ]
         ) grants
-        && lib.length (lib.filter lib.isList (builtins.split "path \"" s)) == 4
+        && lib.length (lib.filter lib.isList (builtins.split "path \"" s)) == 8
         && !(lib.hasInfix "secret/data/swarm/agents/*" s)
         && !(lib.hasInfix "secret/data/swarm/hives" s)
         && !(lib.hasInfix "secret/data/swarm/services/*" s)