fix: use InvalidTokenError instead of generic Error in MockTokenVerifier #138
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The SDK's `requireBearerAuth` middleware only converts `InvalidTokenError` instances to HTTP 401 responses. Generic `Error` instances fall through as HTTP 500, which prevents clients from detecting authentication failures and initiating the OAuth refresh/re-auth flow. This was discovered while building token refresh conformance scenarios — the mock server was returning 500 for expired/invalid tokens instead of the expected 401. Co-authored-by: Cursor <cursoragent@cursor.com>
jdmaturen
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Feb 9, 2026
Add two new client auth conformance scenarios that test OAuth 2.1 refresh token behavior: - `auth/token-refresh-basic`: Tests that clients use the refresh_token grant to obtain a new access token when the current one expires (OAuth 2.1 §6). Server issues 2-second TTL access tokens + refresh token; client must detect 401, send grant_type=refresh_token, and use the new access token. - `auth/token-refresh-rotation`: Same flow but the server rotates the refresh token on each use (OAuth 2.1 §6.1). Client must store the new refresh token and not reuse the old one. Supporting changes: - `createAuthServer`: Add `issueRefreshToken`, `rotateRefreshTokens`, `accessTokenExpiresIn`, and `onRefreshTokenRequest` options. Add full `grant_type=refresh_token` handler with token validation, rotation, and conformance checks. - `createServer`: Add `perRequestServer` option to create a fresh MCP Server per request. Required for token refresh tests where requests span token expiry boundaries (the default behavior calls server.close() on response end, breaking subsequent requests). - `mockTokenVerifier`: Add token expiration tracking (issuedAt, expiresIn per token). Expired tokens now throw InvalidTokenError with an INFO conformance check, enabling proper 401 responses. - `spec-references`: Add OAUTH_2_1_REFRESH_TOKEN (§6) and OAUTH_2_1_TOKEN_ROTATION (§6.1) references. - `everything-client`: Add `runTokenRefreshClient` that exercises the full refresh flow (connect → request → wait for expiry → request). Depends on modelcontextprotocol#138 (InvalidTokenError fix). Co-authored-by: Cursor <cursoragent@cursor.com>
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Summary
MockTokenVerifier.verifyAccessToken()throwsnew Error('Invalid token')for unrecognized tokens, but the SDK'srequireBearerAuthmiddleware only convertsInvalidTokenErrorinstances to HTTP 401 responses. GenericErrorfalls through as HTTP 500.InvalidTokenErrorfrom@modelcontextprotocol/sdk/server/auth/errors.jsand throw it instead.How it was found
While building token refresh conformance scenarios (access token expires → client gets 401 → uses refresh_token grant), the mock server was returning 500 instead of the expected 401 for expired tokens. Traced to this generic
Errorthrow in the verifier.Test plan
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