Adds a minimal RFC 8414 + RFC 6749 client_credentials flow so claude.ai's
custom-MCP integration (no static-Bearer field in the UI) can exchange a
client_id + client_secret pair for the existing BRAIN_MCP_TOKEN and use
it as a Bearer on /mcp. No JWTs, no refresh, no expiry — the rest of
the auth middleware is unchanged.
New package ingestion/internal/oauth:
- MetadataHandler(issuer): serves /.well-known/oauth-authorization-server
with grant_types=[client_credentials] and both
token_endpoint_auth_methods (post + basic).
- TokenHandler(cfg): serves /oauth/token. Validates client_id and
client_secret via constant-time compare; returns BRAIN_MCP_TOKEN as
access_token. RFC 6749 §5.2 error JSON on bad grant / bad creds.
Wiring in cmd/server/main.go: opt-in by setting both OAUTH_CLIENT_ID and
OAUTH_CLIENT_SECRET. Setting only one is misconfiguration → exit 1.
Mounts both endpoints with no auth; MCP_RESOURCE_URL supplies the
issuer.
Also pivots issue #8's vector backend from Qdrant to pgvector (see
DECISIONS.md 2026-05-18) — Qdrant was never deployed and postgres18 with
pgvector already runs as the project default; supersedes 2026-04-08 for
this use case.
Tests cover post-auth, basic-auth, wrong secret, bad grant, GET
rejection, malformed Basic header, and Basic without colon.
Closes hyperguild#5.
58c57412a9