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fix: open CORS for OAuth register/authorize + correct WWW-Authenticate PRM path

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Two follow-up fixes after the SDK auth migration:

1. CORS for browser-based OAuth clients (ChatGPT DCR 403)
   The global cors({ origin: false }) intercepts OPTIONS preflight for
   /oauth/register and /oauth/authorize before the SDK's own cors()
   middleware inside clientRegistrationHandler/authorizationHandler
   runs, causing the browser to reject the response with no
   Access-Control-Allow-Origin header. ChatGPT's connector makes DCR
   from the browser, so this manifested as a 403.
   Fix: extend the open-CORS pre-middleware to also cover
   /oauth/register and /oauth/authorize (same pattern as /.well-known).

2. WWW-Authenticate resource_metadata URL (RFC 9728 §5)
   The MCP handler was advertising the base PRM path
   (/.well-known/oauth-protected-resource) instead of the path-aware
   variant (/.well-known/oauth-protected-resource/mcp). RFC 9728
   requires the resource path to be appended when the resource URI has
   a path component. The SDK registers the path-aware URL; the
   WWW-Authenticate header now points to the same location.
This commit is contained in:
jubnl
2026-05-05 13:29:40 +02:00
parent 86129bbfbc
commit fb6eaaf06d
2 changed files with 13 additions and 4 deletions
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server/src/app.ts
+11 -3
View File
@@ -95,11 +95,19 @@ export function createApp(): express.Application {
const hstsActive = shouldForceHttps || process.env.NODE_ENV === 'production';
const hstsIncludeSubdomains = process.env.HSTS_INCLUDE_SUBDOMAINS === 'true';
// RFC 8414 / RFC 9728: discovery docs are world-readable — open CORS regardless of deployment config
// Covers both the base path and the RFC 9728 path-based variant (/.well-known/oauth-protected-resource/mcp)
// RFC 8414 / RFC 9728 / RFC 7591: discovery docs and DCR are world-readable/writable —
// open CORS for external MCP clients regardless of the deployment's ALLOWED_ORIGINS config.
// /oauth/register and /oauth/authorize need it because browser-based clients (ChatGPT, etc.)
// send a CORS preflight that the global cors({ origin: false }) would answer WITHOUT
// Access-Control-Allow-Origin, causing the browser to reject the response before the
// SDK's own cors() middleware inside clientRegistrationHandler/authorizationHandler runs.
app.use(
(req: Request, _res: Response, next: NextFunction) => {
if (req.path.startsWith('/.well-known/oauth-')) {
if (
req.path.startsWith('/.well-known/oauth-') ||
req.path === '/oauth/register' ||
req.path === '/oauth/authorize'
) {
cors({ origin: '*', credentials: false })(req, _res, next);
} else {
next();