---
id: review-002-prj16-schema-via-call
name: Block Internal-op schema disclosure via services/schema over /call (PRJ-16, cross-crate CF-004)
status: completed
depends_on: []
scope: moderate
risk: medium
impact: project
level: implementation
tags: [gateway, security, review-002, cross-crate]
---

## Description

Review 002 PRJ-16 [major, security]. Internal/ACL-restricted op specs
are readable through the *op* path even though the GET `/schema` route
was fixed in review-001 (SRV-02):

- `call_handler` (`src/gateway/routes.rs:120-133`) pre-checks only the
  **outer** op name — `services/schema` is External with default ACL,
  so the pre-check passes.
- `registry.invoke` dispatches to alkcall's `services_schema_handler`
  (`alkcall src/registry/discovery.rs:327-343`), which does a bare
  `registry.registration(name)` → `spec_to_json` with **no visibility
  and no AccessControl check**.

`POST /call {"operation":"services/schema","input":{"name":"secret/op"}}`
→ the full spec (input/output/error schemas + required_scopes) of any
Internal op, unauthenticated. Same hole via the MCP `call` tool. The
regenerated to_openapi doc asserts "Internal (hidden from HTTP
discovery, GW-02)" — currently false at runtime. The alkcall-side
instance is filed as **CF-004** in
`alkcall/docs/reviews/consumer-findings-ledger.md` (the handler-level
fix there is the complete one; this task is the alkhttp-local layer).

## Acceptance Criteria

- [ ] alkhttp-side guard: before dispatch, when the requested
      operation resolves to a `services/schema`-family handler, apply
      the same is_internal_op + access_check_for_op pre-checks to the
      **inner `name` input** as GET `/schema` does (404 for Internal,
      403 for ACL denial, mirroring routes.rs:151-156)
- [ ] Implementer's choice on mechanism (options: a dispatch-path hook
      in `call_handler`/`batch_handler`/`subscribe_handler`; an
      alkhttp-side wrapper around the registry that intercepts
      `services/schema` inputs; a GatewayDispatch-level check) — the
      invariant is transport-level: **no alkhttp transport may fetch a
      spec the GET `/schema` route would deny for the same identity**
- [ ] Test matrix mirroring the GET /schema tests: `/call` on
      services/schema{internal-op} → 404; unauthorized identity →
      403; MCP `call` tool with the same input → same result
      (feature-gated `mcp` test)
- [ ] A comment/ADR-note recording that the complete fix is
      alkcall-side (CF-004) and this task is the local layer — when
      CF-004 lands, the alkhttp guard becomes defense-in-depth (do NOT
      remove it; the per-transport check stays)
- [ ] `cargo test`, `cargo clippy --all-targets -- -D warnings`,
      `cargo fmt --check` pass (plus `--all-features` if the mcp test lands)

## References

- docs/reviews/002-post-remediation-review.md (Part F', PRJ-16)
- alkcall/docs/reviews/consumer-findings-ledger.md (CF-004, filed 2026-08-30)
- alkcall/src/registry/discovery.rs:327-343 (the unchecked handler)
- src/gateway/routes.rs:120-133 (outer-name-only pre-check), 151-156 (the correct GET /schema checks to mirror)
- docs/architecture/decisions/015-privilege-model-and-authority-context.md

## Notes

The three gateway invoke routes (`/call`, `/batch`, `/subscribe`) all
dispatch through the same spine, so a single interception point (if
found) covers all three + MCP; if the mechanism is route-local, mirror
it in all three pre-check sites. Do not block on the alkcall fix —
this task is shippable independently and the alkcall lead time is
unknown. If CF-004 lands first, re-scope this task to defense-in-depth
assertions only.

## Summary

Dispatch-spine guard: invoke/invoke_streaming apply GET /schema's is-internal + ACL checks to the inner services/schema name (404/FORBIDDEN); shared check also used by the MCP schema tool (deduped). ADR-071 records CF-004 layering (complete fix alkcall-side; guard stays as defense-in-depth).