feat(mcp): OAuth 2.0 Authorization Server for claude.ai connector (#2418)

* feat(mcp): add OAuth 2.0 Authorization Server for claude.ai connector

Implements spec-compliant MCP authentication so claude.ai's remote connector
(which requires OAuth Client ID + Secret, no custom headers) can authenticate.

- public/.well-known/oauth-authorization-server: RFC 8414 discovery document
- api/oauth/token.js: client_credentials grant, issues UUID Bearer token in Redis TTL 3600s
- api/_oauth-token.js: resolveApiKeyFromBearer() looks up token in Redis
- api/mcp.ts: 3-tier auth (Bearer OAuth first, then ?key=, then X-WorldMonitor-Key);
  switch to getPublicCorsHeaders; surface error messages in catch
- vercel.json: rewrite /oauth/token, exclude oauth from SPA, CORS headers
- tests: update SPA no-cache pattern

Supersedes PR #2417. Usage: URL=worldmonitor.app/mcp, Client ID=worldmonitor, Client Secret=<API key>

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* docs: fix markdown lint in OAuth plan (blank lines around lists)

* fix(oauth): address all P1+P2 code review findings for MCP OAuth endpoint

- Add per-IP rate limiting (10 req/min) to /oauth/token via Upstash slidingWindow
- Return HTTP 401 + WWW-Authenticate header when Bearer token is invalid/expired
- Add Cache-Control: no-store + Pragma: no-cache to token response (RFC 6749 §5.1)
- Simplify _oauth-token.js to delegate to readJsonFromUpstash (removes duplicated Redis boilerplate)
- Remove dead code from token.js: parseBasicAuth, JSON body path, clientId/issuedAt fields
- Add Content-Type: application/json header for /.well-known/oauth-authorization-server
- Remove response_types_supported (only applies to authorization endpoint, not client_credentials)

Closes: todos 075, 076, 077, 078, 079

🤖 Generated with claude-sonnet-4-6 via Claude Code (https://claude.ai/claude-code) + Compound Engineering v2.40.0

Co-Authored-By: claude-sonnet-4-6 (200K context) <noreply@anthropic.com>

* chore(review): fresh review findings — todos 081-086, mark 075/077/078/079 complete

* fix(mcp): remove ?key= URL param auth + mask internal errors

- Remove ?key= query param auth path — API keys in URLs appear in
  Vercel/CF access logs, browser history, Referer headers. OAuth
  client_credentials (same PR) already covers clients that cannot
  set custom headers. Only two auth paths remain: Bearer OAuth and
  X-WorldMonitor-Key header.

- Revert err.message disclosure: catch block was accidentally exposing
  internal service URLs/IPs via err.message. Restore original hardcoded
  string, add console.error for server-side visibility.

Resolves: todos 081, 082

* fix(oauth): resolve all P2/P3 review findings (todos 076, 080, 083-086)

- 076: no-credentials path in mcp.ts now returns HTTP 401 + WWW-Authenticate instead of rpcError (200)
- 080: store key fingerprint (sha256 first 16 hex chars) in Redis, not plaintext key
- 083: replace Array.includes() with timingSafeIncludes() (constant-time HMAC comparison) in token.js and mcp.ts
- 084: resolveApiKeyFromBearer uses direct fetch that throws on Redis errors (500 not 401 on infra failure)
- 085: token.js imports getClientIp, getPublicCorsHeaders, jsonResponse from shared helpers; removes local duplicates
- 086: mcp.ts auth chain restructured to check Bearer header first, passes token string to resolveApiKeyFromBearer (eliminates double header read + unconditional await)

* test(mcp): update auth test to expect HTTP 401 for missing credentials

Align with todo 076 fix: no-credentials path now returns 401 + WWW-Authenticate
instead of JSON-RPC 200 response. Also asserts WWW-Authenticate header presence.

* chore: mark todos 076, 080, 083-086 complete

* fix(mcp): harden OAuth error paths and fix rate limit cross-user collision

- Wrap resolveApiKeyFromBearer() in try/catch in mcp.ts; Redis/network
  errors now return 503 + Retry-After: 5 instead of crashing the handler
- Wrap storeToken() fetch in try/catch in oauth/token.js; network errors
  return false so the existing if (!stored) path returns 500 cleanly
- Re-key token endpoint rate limit by sha256(clientSecret).slice(0,8)
  instead of IP; prevents cross-user 429s when callers share Anthropic's
  shared outbound IPs (Claude remote MCP connector)

---------

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

api/_crypto.js

@@ -0,0 +1,24 @@
+export async function sha256Hex(str) {
+  const buf = await crypto.subtle.digest('SHA-256', new TextEncoder().encode(str));
+  return Array.from(new Uint8Array(buf)).map(b => b.toString(16).padStart(2, '0')).join('');
+}
+
+export async function keyFingerprint(key) {
+  return (await sha256Hex(key)).slice(0, 16);
+}
+
+export async function timingSafeIncludes(candidate, validKeys) {
+  if (!candidate || !validKeys.length) return false;
+  const enc = new TextEncoder();
+  const candidateHash = await crypto.subtle.digest('SHA-256', enc.encode(candidate));
+  const candidateBytes = new Uint8Array(candidateHash);
+  let found = false;
+  for (const k of validKeys) {
+    const kHash = await crypto.subtle.digest('SHA-256', enc.encode(k));
+    const kBytes = new Uint8Array(kHash);
+    let diff = 0;
+    for (let i = 0; i < kBytes.length; i++) diff |= candidateBytes[i] ^ kBytes[i];
+    if (diff === 0) found = true;
+  }
+  return found;
+}