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c737789b26
* feat(mcp): discover the OBO token endpoint via RFC 9728 to RFC 8414 (no IdP guessing) An oauth2_token_exchange server can now have its token endpoint discovered the same way the oauth2 (authorization_code) flow already does, instead of always requiring token_exchange_endpoint/token_url to be configured by hand. The existing _descovery_metadata chain (RFC 9728 protected-resource metadata -> RFC 8414 authorization-server metadata -> token_endpoint, SSRF-guarded via async_safe_get) is reused; both the config-load and DB-build paths gate on a new _obo_needs_endpoint_discovery so discovery runs only when no endpoint is configured, and an explicitly configured endpoint still wins and skips the round-trip. The discovered token endpoint lands on token_url, which _token_exchange_spec already reads, so no resolver change is needed. _resolve_oauth2_flow returns None for any non-oauth2 auth_type, so a discovered token_url on an OBO server is never mis-inferred as the M2M client_credentials flow. Discovery for OBO is authoritative only: the resolution order is explicitly configured endpoint, then RFC 9728 -> RFC 8414 advertisement, then fail closed (412, on the parent commit). The gateway never guesses the IdP. _descovery_metadata grows an allow_origin_fallback flag, kept True for the browser oauth2 flow (a human sees the redirect) but set False for token_exchange so the last-resort guess that treats the resource server's own origin as its authorization server is skipped; a subject token is never exchanged against an inferred endpoint. * fix(mcp): surface a failed OBO exchange at connect instead of an empty tool list A token_exchange server whose exchange fails with a subject present used to open the MCP session anyway and mask the failure as an empty tools/list. Single-server routes now run the exchange preemptively at the transport edge, where a rejected subject raises the RFC 9728 challenge and a gateway fault its public status; the multi-server aggregate keeps absorbing per-server auth failures. The exchanger caches the preflight result, so the session's list/call reuses it with no extra IdP round-trip. Discovery now also debug-logs the authorization server's advertised issuer, grant types, and client auth methods * fix(mcp): persist the discovered OBO token endpoint to the DB row A DB-backed oauth2_token_exchange server with no configured endpoint had its token_url resolved via RFC 9728 -> RFC 8414 only on the in-memory object returned from build_mcp_server_from_table; the row kept token_url=None, so every rebuild re-ran discovery and a transient upstream outage during a rebuild left the server with no endpoint until the next successful discovery. Write the discovered token_url back onto the row so the guard sees it on the next build. Best-effort and scoped to DB servers: config servers already persist in-memory, and the write-back never fires from a user connect (only from add/update/reload, all admin or system driven). Adds DB-path coverage for discovery firing when unset, skipping when the credentials endpoint is configured, the write-back, and its negative guards |
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