# Dashboard EventsHub per-session ACL (TST-15 / SEC-25 · session-resilience epic Phase 4)

Status: **Design** — approved-to-implement pending the schema-touch call in §9.
Findings: TST-15 (`Medium`, P2), SEC-25 (`Low`, P2). Epic tasks: 16–19 of
`docs/plans/2026-06-15-session-resilience.md`.
Depends on: TST-02 (owner-scoped gRPC attach, shipped P0), SEC-25 near-term
mitigation (value redaction in the dashboard mirror, shipped P2).

## 1. Problem

`EventsHub.SubscribeSession(sessionId)` joins the caller's SignalR connection to
the `session:{id}` group with no per-session check. The hub-level
`[Authorize(Policy = HubClientsPolicy)]` only requires *any* dashboard role, so
**every authenticated Viewer (and, via SEC-02, anonymous localhost) can subscribe
to any session's raw `MxEvent` feed** — the one production-source `TODO` left in
the repo (`Dashboard/Hubs/EventsHub.cs:42`).

SEC-25's shipped mitigation already strips tag *values* from the mirrored events
when `Dashboard:ShowTagValues` is false (the default), so no payload leaks through
this seam today. What remains is **event-metadata visibility**: which sessions'
event streams (worker sequence, family, server/item handles, alarm references) a
given Viewer may observe. That is what this ACL gates.

### 1.1 The crux: two disjoint identity domains

This is *not* a copy of the gRPC owner check (TST-02), and the reason is the whole
design problem:

| | gRPC `StreamEvents` (TST-02) | Dashboard EventsHub (TST-15) |
|---|---|---|
| Caller identity | API key (`mxgw_<id>_<secret>`) | LDAP user → `Administrator`/`Viewer` role |
| Session identity | `GatewaySession.OwnerKeyId` (an API key id) | same session, but caller has **no** key id |
| Check | `caller.KeyId == session.OwnerKeyId` — same domain, trivial | caller is an LDAP principal; there is **nothing on the session to compare it to** |

TST-02's binding is API-key-id ↔ API-key-id. A dashboard Viewer has no API key id,
so "sessions they own" does not translate directly. The design must introduce a
**bridge concept** that both a *session* and a *dashboard group* can be associated
with. That bridge is the **session tag** (epic Task 17, "Session Tag + dashboard
group-to-tag config").

## 2. Decision summary

1. **Admin sees all.** A connection carrying `DashboardRoles.Admin` bypasses the
   ACL entirely — it may subscribe to any session. (Admin already reaches every
   destructive surface; event-metadata visibility is strictly weaker.)
2. **Viewer is strict.** A Viewer-only connection may subscribe to a session iff
   `session.Tags ∩ viewer.GrantedTags ≠ ∅`.
3. **A session's tags come from its owning API key**, not from the client wire
   request. The API key is the tenant principal (TST-02 already treats it as the
   session's owner); deriving the tag from the key makes the dashboard boundary
   match the gRPC owner boundary. See §3.1 and the rejected alternative in §10.1.
4. **Untagged sessions are Admin-only by default.** If the owning key carries no
   tag, no Viewer sees the session. A config knob
   (`Dashboard:UntaggedSessionVisibility`) can relax this to `AllViewers` for a
   genuinely single-tenant deployment, preserving today's behaviour for operators
   who want it. Default is the safe `AdminOnly`.
5. **Enforcement is server-side and stateless**, carried in the existing
   short-lived hub bearer token (§4). No new server-side session/among-connection
   state.

## 3. The session tag

A session gains an immutable set of tags, assigned once at `OpenSession` and never
changed for the session's life (so no re-check on an already-joined SignalR
group is needed).

```csharp
// GatewaySession — new read-only property, set from the owner key at construction.
public IReadOnlySet<string> Tags { get; }   // empty set == untagged
```

### 3.1 Source: the owning API key

Sessions inherit the tag set of the API key that opened them. The tag rides in the
**existing `ApiKeyConstraints` JSON blob** (`ApiKeyConstraintSerializer`), so there
is **no SQLite schema migration** — a new column is not required:

```csharp
// ApiKeyConstraints — add one field (serialized into the existing constraints column).
public sealed record ApiKeyConstraints(
    ...,
    bool ReadHistorizedOnly,
    IReadOnlyList<string> DashboardTags);   // NEW — default empty
```

At `OpenSession`, the resolved `ApiKeyIdentity.EffectiveConstraints.DashboardTags`
is copied onto the new `GatewaySession.Tags`. The `apikey` admin CLI gains
`--dashboard-tags team-a,team-b` on `create`/`update`.

Semantic note: `ApiKeyConstraints` today scopes *data-access* authorization
(read/write subtrees, globs, classification). A dashboard *visibility* tag is a
distinct concern, but piggy-backing on the same serialized blob is the pragmatic
choice — it avoids a migration and keeps all per-key policy in one place. The
field is documented as visibility-only; it does **not** gate any data-access path.

### 3.2 Dashboard group → tag grant

A new config map, mirroring the shape of `Dashboard:GroupToRole`:

```jsonc
"MxGateway": {
  "Dashboard": {
    "GroupToRole": { "GwAdmin": "Administrator", "GwViewer": "Viewer" },
    "GroupToTag":  { "GwViewer": ["team-a"], "TeamBViewers": ["team-b"] },
    "UntaggedSessionVisibility": "AdminOnly"   // or "AllViewers"
  }
}
```

`GroupToTag` maps an LDAP group (short RDN, matching the `GroupToRole` convention
in `DashboardGroupRoleMapping`) to the tags that group is granted. A Viewer's
`GrantedTags` is the union over their LDAP groups. Admin's grant is irrelevant
(they bypass). Bound on `DashboardOptions`:

```csharp
public Dictionary<string, string[]> GroupToTag { get; init; }
    = new(StringComparer.OrdinalIgnoreCase);
public UntaggedSessionVisibility UntaggedSessionVisibility { get; init; }
    = UntaggedSessionVisibility.AdminOnly;
```

Validated in `GatewayOptionsValidator` exactly like `GroupToRole` (keys non-empty;
`UntaggedSessionVisibility` a known enum). No validation coupling to `GroupToRole`
— a group may appear in one, the other, or both.

## 4. Enforcement path

The tag grant must reach `SubscribeSession`. A hub connection authenticates by
either the dashboard cookie or the 5-minute bearer minted by `HubTokenService`.
`HubTokenPayload` today carries `(Name, NameIdentifier, Roles)` — extend it with
the resolved granted-tag set:

```csharp
private sealed record HubTokenPayload(
    string? Name, string? NameIdentifier, string[]? Roles, string[]? Tags);
```

- **Mint (`HubTokenService.Issue`)** — resolve the principal's granted tags from
  their LDAP-group claims (`mxgateway:ldap_group`) via a `GroupToTag` mapper
  (sibling of `DashboardGroupRoleMapping`), and stamp them into the payload as a
  `zb:dashboardtag` claim set. Admin needs no tags stamped.
- **Cookie path** — the same tag claims are added in
  `DashboardAuthenticator.CreatePrincipal` so a cookie-authenticated circuit
  carries them without a token round-trip.
- **Validate (`HubTokenService.Validate`)** — rehydrate the tag claims onto the
  reconstructed principal, alongside the existing role claims.
- The 5-minute lifetime already bounds staleness of a changed grant
  (documented at `HubTokenService.cs:30-37`) — this now also bounds a changed
  tag grant, which is the natural place the SEC-25 "tokens gain session binding"
  note anticipated.

`SubscribeSession` becomes an authorizing, `SessionManager`-aware method:

```csharp
public async Task SubscribeSession(string sessionId)
{
    if (string.IsNullOrWhiteSpace(sessionId)) return;

    if (!_sessionAcl.CanViewSession(Context.User, sessionId))
    {
        // Deny quietly: do NOT join the group. Optionally surface a HubException
        // so the client can distinguish "denied" from "no events yet".
        throw new HubException("Not authorized for this session.");
    }

    await Groups.AddToGroupAsync(Context.ConnectionId, GroupName(sessionId));
}
```

`IDashboardSessionAcl.CanViewSession(ClaimsPrincipal, sessionId)`:
1. Admin role → `true`.
2. Session not found in `SessionManager` → `false` (no group join for a phantom id).
3. Session untagged → `UntaggedSessionVisibility == AllViewers`.
4. Otherwise → `session.Tags ∩ principal.GrantedTags ≠ ∅`.

Because the broadcaster only ever publishes to `session:{id}` and only joined
connections receive, gating at join is sufficient — there is no second seam to
guard. Tags are immutable per session, so a mid-life re-check is unnecessary.

### 4.1 Interaction with SEC-02 (anonymous localhost)

Anonymous-localhost satisfies `HubClientsPolicy` but carries no role and no tags.
Under this ACL it is treated as a **Viewer with an empty tag grant** → sees only
untagged sessions, and only when `UntaggedSessionVisibility == AllViewers`. That
tightens SEC-02's current "loopback sees every session" posture without a separate
change. `DisableLogin` auto-login (both roles) keeps admin-sees-all — unchanged.

## 5. End-to-end data flow

```
apikey create --dashboard-tags team-a           →  key.Constraints.DashboardTags = [team-a]
client OpenSession (Bearer mxgw_<id>_..)          →  session.OwnerKeyId = <id>,
                                                       session.Tags = [team-a]
LDAP login  gw-viewer ∈ group GwViewer            →  GroupToTag[GwViewer] = [team-a]
                                                       principal grantedTags = {team-a}
hub token / cookie                                →  payload.Tags = [team-a]
SubscribeSession("s-123")  (session.Tags={team-a})→  {team-a} ∩ {team-a} ≠ ∅  → JOIN
SubscribeSession("s-999")  (session.Tags={team-b})→  {team-a} ∩ {team-b} = ∅  → DENY
Admin                                              →  bypass → JOIN either
```

## 6. Task breakdown (maps to epic Tasks 16–19)

- **Task 16 — gRPC all-sessions admin scope (already largely shipped).** The gRPC
  owner gate is TST-02. This task is the *dashboard* admin bypass in
  `IDashboardSessionAcl` (§4). No gRPC change required; the "all-sessions admin
  scope" for gRPC is out of scope for TST-15 and stays with the broader epic.
- **Task 17 — session tag + group-to-tag config.** `ApiKeyConstraints.DashboardTags`
  + serializer + `apikey` CLI flag; `GatewaySession.Tags` set at `OpenSession`;
  `DashboardOptions.GroupToTag` + `UntaggedSessionVisibility` + validator.
- **Task 18 — EventsHub ACL + hub-token tag claim.** `HubTokenPayload.Tags`,
  mint/validate, cookie-principal tag claims, `IDashboardSessionAcl` +
  `SubscribeSession` gate. Remove the `TODO(per-session-acl)`.
- **Task 19 — ACL tests, incl. live LDAP users.** §7.

Sequence: 17 → 18 → 19; 16's dashboard slice folds into 18.

## 7. Test plan

Unit / fake-worker (default suite, no LDAP, no COM):
- `DashboardSessionAclTests` — the four `CanViewSession` branches: admin bypass;
  session-not-found deny; untagged under both `UntaggedSessionVisibility` values;
  tag-intersection match and non-match.
- `HubTokenServiceTests` — extend: tags round-trip through `Issue`/`Validate`;
  a token minted before a grant change still carries the old tags until expiry.
- `EventsHubTests` — `SubscribeSession` joins on allow, throws `HubException`
  and does **not** join on deny (assert via a fake `IGroupManager`).
- `GroupToTag` mapper tests — union across multiple groups; unknown group → no tags.
- Config: `GatewayOptionsValidator` accepts/ rejects `GroupToTag` /
  `UntaggedSessionVisibility` shapes.

Live LDAP (`MXGATEWAY_RUN_LIVE_LDAP_TESTS=1`, `LiveLdapFactAttribute`) — extend
`DashboardLdapLiveTests`: `gw-viewer`/`password` (Viewer) is granted `team-a` via
`GroupToTag`, subscribes to a `team-a` session (allow) and a `team-b` session
(deny); `multi-role`/`password` (Admin) subscribes to both (allow). Uses the
shared GLAuth server per `glauth.md`.

Verification: `dotnet test ... --filter FullyQualifiedName~DashboardSessionAcl`,
`~EventsHub`, `~HubTokenService`; `dotnet build src/ZB.MOM.WW.MxGateway.Server`.

## 8. Docs to update (same change as source)

- `docs/Sessions.md` — dashboard event visibility / session-tag model.
- `gateway.md` dashboard section — the ACL and the tag source.
- `docs/GatewayConfiguration.md` — `Dashboard:GroupToTag`,
  `Dashboard:UntaggedSessionVisibility`; `apikey --dashboard-tags`.
- `docs/Authorization.md` — note `DashboardTags` is visibility-only, not a
  data-access constraint.
- `CLAUDE.md` dashboard-auth paragraph — Viewer is tag-scoped; Admin sees all;
  anonymous-localhost is an empty-grant Viewer.
- `glauth.md` — the test-user tag grants used by the live tests.

## 9. Open call for the implementer

**Does the tag ride in the existing `ApiKeyConstraints` JSON blob (no migration,
recommended) or a new dedicated key column/table?** The blob avoids a SQLite
migration and keeps per-key policy in one place; a dedicated column is cleaner
semantically (visibility ≠ data-access constraint) but costs a migration + audit
touch. Recommendation: **blob**, documented as visibility-only. Settle before
Task 17.

## 10. Rejected alternatives

### 10.1 Client-supplied session tag (proto field on `OpenSession`)
Lighter — one proto field, one session field, no API-key-store touch. Rejected as
*primary* because the tag would then be attacker-controlled: a low-trust gRPC
client could label its session with any tenant's tag, choosing which dashboard
groups observe its event feed. Deriving the tag from the owning API key keeps the
boundary aligned with TST-02's trust model (the key is the tenant). (If a future
requirement wants client-declared sub-tags *within* an owner's grant, they can be
intersected with the key's tags — additive, not a replacement.)

### 10.2 Map dashboard groups directly to owner key ids (reuse `OwnerKeyId`, no tag)
Zero API-key-store change — `Dashboard:GroupToOwnerKeys` maps a group to a set of
key ids. Rejected: key ids are opaque and rotate; operators would maintain a map
of GUID-like ids, and every key rotation breaks the dashboard grant. A named tag
is the right operator-facing abstraction and survives key rotation.

### 10.3 Full jti-denylist token revocation
Out of scope. The 5-minute token lifetime bounds a changed grant; the tokens are
data-protection-encrypted and single-purpose. Matches the SEC-25 recommendation
to defer heavy revocation.

## 11. Security considerations

- **No new value-leak surface.** SEC-25 already redacts values in the mirror; this
  change only narrows *which sessions'* metadata a Viewer sees. Strictly a
  tightening.
- **Fail closed.** Session-not-found, empty grant, and untagged-under-`AdminOnly`
  all deny. A misconfigured/empty `GroupToTag` yields Viewers who see nothing
  (except untagged-under-`AllViewers`) — safe, not open.
- **Default preserves single-tenant ergonomics** only if the operator opts into
  `UntaggedSessionVisibility=AllViewers`; the shipped default (`AdminOnly`) is the
  strict one, so an upgrade tightens rather than loosens.
- **Staleness bound.** A revoked tag grant takes effect within one token lifetime
  (≤5 min) for token-auth connections and immediately for a fresh cookie login.
```