feat(cimd): standalone Client ID Metadata Document publisher

[omrishiv]

Refs: #992 (publisher slice — see Not covered below; does not close it)
Parent epic: #988 (Phase 4 CIMD)

What

Publishes the registry's own Client ID Metadata Document (CIMD) so the registry can identify itself as an OAuth client (by URL) to external CIMD-aware IdPs, without pre-registration or DCR. Per the CIMD draft, the document's URL is the client_id.

GET /oauth/client-metadata.json      # public, unauthenticated, cacheable

Opt-in (CIMD_PUBLISHER_ENABLED, default off → 404). Returns client_id, client_name, client_uri, redirect_uris, grant_types, response_types, token_endpoint_auth_method: none, scope, and optional logo_uri/contacts, with Cache-Control: public, max-age=<CIMD_CACHE_TTL>.

Why this is a standalone branch

The original CIMD work was built on top of #1692 (the gateway token proxy), which was closed. The CIMD publisher has no functional dependency on the token proxy — it references no token-proxy symbols. This branch is the publisher rebased cleanly onto main, so #992's publisher can land independently of the closed token-proxy effort. (The token-proxy-coupled bits from the original branch — the TestCimdClientIdPassthrough tests and the python-multipart dep — were intentionally dropped; they belong with a token proxy, not the publisher.)

Design decisions

• Path /oauth/client-metadata.json, not /.well-known/…. A CIMD is a client-published resource at an operator-chosen public path — RFC 8615 .well-known is for authority/server documents,. /oauth/client-metadata.json matches the MCP spec's own example and the AT-Protocol convention. [Phase 4] Publish CIMD (Client ID Metadata Document) for AI Registry Tools MCP client #992 explicitly left the path "TBD, track the draft," so this satisfies that note rather than contradicting it.
• Root-mounted, rides the public catch-all. The route is served by a root-mounted cimd_router; the gateway nginx catch-all location / proxies to the registry with no auth_request, so the AS fetches it unauthenticated with zero nginx changes.
• client_id/redirect_uris derive from the egress OAuth callback base (settings.egress_oauth_callback_base = EGRESS_OAUTH_CALLBACK_BASE_URL or REGISTRY_URL), not registry_url alone — so a deployment whose external callback host differs from registry_url still publishes a client_id and redirect that share the origin the IdP redirects back to. A single canonical build_cimd_client_id_url guarantees the published URL and any future outbound client_id can't drift.
• Kept the safe defaults: opt-in gate, enforce_https on the client_id, and public, max-age caching.

Config surface (three-surface parity)

All 7 registry-consumed, non-secret params are wired first-class:

Env	Setting	Helm (registry.app.*)	Terraform var	Type / default
CIMD_PUBLISHER_ENABLED	cimd_publisher_enabled	cimdPublisherEnabled	cimd_publisher_enabled	bool / false
CIMD_CACHE_TTL	cimd_cache_ttl	cimdCacheTtl	cimd_cache_ttl	int / 3600
CIMD_CLIENT_NAME	cimd_client_name	cimdClientName	cimd_client_name	str / "AI Registry Tools"
CIMD_REDIRECT_URIS	cimd_redirect_uris	cimdRedirectUris	cimd_redirect_uris	str CSV / ""
CIMD_SCOPE	cimd_scope	cimdScope	cimd_scope	str / ""
CIMD_LOGO_URI	cimd_logo_uri	cimdLogoUri	cimd_logo_uri	str / ""
CIMD_CONTACTS	cimd_contacts	cimdContacts	cimd_contacts	str CSV / ""

• System Config UI: new CIMD Publisher group in config_routes.py CONFIG_GROUPS (all non-sensitive).
• Docs: row block in docs/unified-parameter-reference.md.
• Docker: .env.example + all three compose files (typed ${VAR:-false}/${VAR:-3600} defaults so an empty value never breaks Pydantic).
• Helm: charts/registry values + deployment (bool/int via toString | quote) + reserved-env-names.txt (chart-managed, not extraEnv-shadowable).
• Terraform: root + module variables, module passthrough, ecs-services.tf env (bool/int via tostring()), terraform.tfvars.example.

Testing

• tests/integration/test_cimd_publisher.py — document shape, required fields, field-order stability, cache header, client_id == served URL parity, callback-base precedence over registry_url, disabled→404, and a root-mount/no-prefix invariant that reads main.py so a future rename/prefix can't silently break parity. 6 passed.
• Helm helm template charts/registry renders CIMD_PUBLISHER_ENABLED: "true", CIMD_CACHE_TTL: "1200" (bool/int coercion correct).
• Terraform terraform fmt -check clean on all .tf files.
• ruff check/format, pre-commit (syntax, fast tests) clean.

Not covered by this PR (so #992 is not closed by mistake)

1. Outbound client_id wiring — nothing today sends the registry's CIMD URL as its client_id on an outbound /authorize (egress uses per-server operator credentials). There is no such flow to wire yet; build_cimd_client_id_url is the single source of truth the future outbound path must reuse. [Phase 4] Publish CIMD (Client ID Metadata Document) for AI Registry Tools MCP client #992 frames this as forward-looking ("once AI Registry Tools calls external MCP servers").
2. Fake-AS end-to-end ([Phase 4] Publish CIMD (Client ID Metadata Document) for AI Registry Tools MCP client #992 acceptance) — a test of that outbound flow; can't be written until (1) exists.
3. [Phase 4] CIMD consumer: accept CIMD URL as client_id on /authorize #993 (CIMD consumer) — accepting a CIMD URL as client_id on /authorize//oauth/token is not in this branch. The original approach ("Option Y": the token proxy forwards client_id verbatim to the upstream IdP) depended on [Phase 3] RFC 8707 resource enforcement + gateway token proxy (IdP-signed MCP tokens) #1692's token proxy, which was dropped here. [Phase 4] CIMD consumer: accept CIMD URL as client_id on /authorize #993 returns with the token-proxy / OAuth-discovery track.

Files

20 files, +518 / −7. Publisher core: registry/auth/oauth_metadata.py, registry/api/wellknown_routes.py, registry/main.py, registry/core/config.py. Surface wiring + docs + tests as above.

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