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c5f50e817b## Summary DNS auth users have repeatedly hit two failure modes that both produce the same opaque "Ed25519 signature verification failed" error, making them indistinguishable to debug. This PR makes both diagnosable end-to-end without changing the auth protocol or any successful path. The two recurring failure modes: 1. **Wrong placement** — TXT record put under a selector (`_mcp-auth.<domain>` or `_mcp-registry.<domain>`) instead of the apex. DKIM-style intuition, but MCP DNS auth uses SPF-style apex placement. See #385 (PR #388 fixed the docs but the failure recurred), #1103, #1126. 2. **Stale apex record** — old TXT record left behind after a key rotation, silently tried first and rejected. ## Changes **`internal/api/handlers/v0/auth/dns.go`** — when the apex has no `v=MCPv1` record, probe `_mcp-auth.<domain>` and `_mcp-registry.<domain>` in parallel (2s individual timeout). If a record is found there, return a targeted error pointing the user at the apex. Costs zero extra DNS work in the success path. **`internal/api/handlers/v0/auth/common.go`** — when verification fails against records that *are* present, include short fingerprints of every key the registry tried (`ed25519:YJLsHFhu`-style 8-char prefix). A new `ErrSignatureMismatch` sentinel keeps structural errors (wrong signature size, unsupported algorithm) passing through unchanged via `errors.Is`, so existing assertions on those messages still hold. **`docs/modelcontextprotocol-io/authentication.mdx`** — anti-pattern `<Warning>` callout in the DNS section explicitly warning against selector placement and stale records. **Tests** — two new tests: - `TestDNSAuthHandler_WrongSelectorProbe` — verifies the probe surfaces records found at `_mcp-auth.` / `_mcp-registry.` and falls through to the standard error when nothing is found anywhere - `TestDNSAuthHandler_StaleKeyFingerprintInError` — verifies the fingerprint hint appears in the failure message for #1126's exact scenario One existing test assertion was updated from a generic `"signature verification failed"` substring to the more specific `"invalid signature size for ECDSA P-384"` it should always have been asserting; the new sentinel-based logic surfaces structural errors verbatim. ## Test plan - [x] `make lint` — clean - [x] `make test-unit` — all auth tests pass (existing + 2 new) - [x] Verified existing single-key and multi-key paths preserve their original (more specific) error messages where they were already specific - [ ] Reviewer to sanity-check the docs callout renders well in the Mintlify theme ## Out of scope The publisher-side preflight DNS check (cross-link in #845) is intentionally **not** in this PR — that belongs in the broader CLI UX work tracked by #845. Refs #845, #385, #1103 Fixes #1126 --------- Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com> |
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MCP Registry Documentation
The MCP registry provides MCP clients with a list of MCP servers, like an app store for MCP servers.
I want to...
- 📤 Publish my MCP server → Publishing Guide
- 📥 Consume registry data → API Usage Guide
- 🔌 Understand the registry's purpose → Ecosystem vision
- 📋 Look up specific information → server.json spec | API spec | CLI reference
- 🤝 Add reference to my community project → Community Projects
Documentation Index
- 📄 Public-facing docs - Published on modelcontextprotocol.io
- 🏗️ Design documentation - Architecture, vision, and roadmap
- 📖 Reference - Technical specifications
- 🔧 Contributing guides - How to contribute
- 🔒 Administration - Admin operations