Critical: the MCP SDK auto-enables DNS-rebinding protection when its host
parameter is left at the 127.0.0.1 default, hard-coding a loopback-only Host
allow-list. Every remote client (the only deployment this feature targets) was
refused with HTTP 421 before auth or the tool ran. Now driven by a new
MCP_ALLOWED_HOSTS setting, with '*' as an explicit, logged opt-out.
Also bounds query/top_k to match AskRequest (top_k is amplified 4x downstream,
so an unbounded value was a resource-exhaustion vector), decodes the
Authorization header as latin-1 per the ASGI spec instead of raising a 500 on
malformed bytes, and returns WWW-Authenticate on 401 per RFC 7235.
Moves the psycopg2 import guard into backend/tests/conftest.py: duplicated
across four test modules, it only worked because of alphabetical collection
order, and any earlier-sorting package would have reintroduced a live
connection attempt against the production database.
Registers the mcp module in the authoritative backend architecture doc.
84 backend tests pass. Verified against a live server: allowed remote Host
returns a valid initialize result, unknown Host returns 421, missing token
returns 401 with WWW-Authenticate.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
- New backend/app/mcp/ module: MCPServer instance with a single
search_regulations tool backed by the existing AgentConversationService.
- MCPAuthMiddleware reuses existing JWT auth (no new auth mechanism).
- Mounted at /mcp/ in api/main.py via Streamable HTTP transport; wired the
MCP session manager into the existing lifespan() via AsyncExitStack
(app.mount() does not propagate nested ASGI lifespans automatically).
- Fixed a doubled /mcp/mcp path by setting streamable_http_path to "/"
(MCPServer.streamable_http_app() defaults to registering its own /mcp route).
- Verified end-to-end with the real mcp Python client: list_tools() returns
search_regulations, auth correctly 401s without or with an invalid token.
- 7 new tests, 76 total (up from 69), all passing.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
