[Bug]: MCP servers that allow unauthenticated initialize (HTTP 200) never trigger OAuth — e.g. Google's hosted Drive MCP

[yakovyarmo]

What happened?

A streamable-http MCP server configured with requiresOAuth: true never starts the OAuth flow — the Google consent screen is never shown. LibreChat reports the server as "reinitialized successfully," oauthRequired: false, and the token store stays empty. The failure only surfaces later, when a tool is actually executed, as an auth error from the upstream API.

Concrete repro server: Google's official hosted Drive MCP at https://drivemcp.googleapis.com/mcp/v1.

Root cause

LibreChat only initiates OAuth when the MCP server returns HTTP 401/403 on connect:

• MCPConnection.connectClient() emits oauthRequired only from the catch block, gated by isOAuthError(error) (401/403) — packages/api/src/mcp/connection.ts:1116 (matcher at :1503-1538).
• MCPConnectionFactory.getOAuthTokens() finds no stored token, logs "...will trigger OAuth flow", then just returns null — it does not start anything (packages/api/src/mcp/MCPConnectionFactory.ts:283).
• createConnection() then connects unauthenticated and, because the server replies 200, succeeds — so oauthRequired is never emitted (MCPConnectionFactory.ts:226-247).
• reinitMCPServer therefore returns { success: true, oauthRequired: false, oauthUrl: null } (api/server/services/Tools/mcp.js).
• The frontend only opens the consent popup when oauthRequired && oauthUrl (client/src/hooks/MCP/useMCPServerManager.ts:339-348), so nothing happens.

Google's hosted Drive MCP does not follow the 401-challenge pattern. Verified directly with curl (no Authorization header):

• POST initialize → HTTP 200 (returns serverInfo/capabilities)
• POST tools/list → HTTP 200 (returns the full tool list)
• POST tools/call → HTTP 200 with an in-body JSON-RPC error: "Request is missing required authentication credential. Expected OAuth 2 access token..."

It does expose RFC 9728 metadata at /.well-known/oauth-protected-resource/mcp/v1 (authorization_servers: ["https://accounts.google.com/"]), so OAuth is clearly required — it's just never enforced at connect time. Net effect: requiresOAuth: true has effectively no effect for such servers.

Steps to reproduce

1. Configure the server in librechat.yaml:

   mcpServers:
     google-drive:
       type: streamable-http
       url: https://drivemcp.googleapis.com/mcp/v1
       requiresOAuth: true
       oauth:
         client_id: ${GOOGLE_DRIVE_CLIENT_ID}
         client_secret: ${GOOGLE_DRIVE_CLIENT_SECRET}
         scope: "https://www.googleapis.com/auth/drive.readonly https://www.googleapis.com/auth/drive.file"
         token_url: https://oauth2.googleapis.com/token
         authorization_url: https://accounts.google.com/o/oauth2/v2/auth?access_type=offline&prompt=consent

   (Redirect URI https://<domain>/api/mcp/google-drive/oauth/callback registered in Google Cloud.)
2. Reinitialize/connect the server in the UI — it reports success, no consent screen.
3. Run a tool → fails: "Request is missing required authentication credential."

Expected behavior

When requiresOAuth: true (or oauth/protected-resource metadata is present) and no valid token exists, LibreChat should proactively start the OAuth flow instead of waiting for a 401 — i.e., treat "OAuth-required server + no token" the same as a 401 challenge.

Suggested fix

When requiresOAuth: true (or oauth/protected-resource metadata is present) and no valid token exists, proactively start the OAuth flow instead of waiting for a 401. LibreChat already discovers RFC 9728 metadata; the gap is only that getOAuthTokens() returns null silently (MCPConnectionFactory.ts:283) and oauthRequired is emitted solely from the 401 catch path (connection.ts:1116). Trigger it in the user-connection path (MCPConnectionFactory.createConnection), gated so tool discovery (discoverToolsInternal) and app-level startup connections still list tools unauthenticated.

This mirrors the fix being made in Dify for the identical server/behavior (see Related).

Related

• [Bug]: MCP Server requiring OAuth not starting auth flow #9657 (closed, unresolved) — same root cause, Google's BigQuery MCP Toolbox.
• MCP OAuth flow never triggers for servers that return 200 OK on initialize without auth (Google Drive MCP) langgenius/dify#36230 (open) — identical bug in another MCP client with the same server (drivemcp.googleapis.com/mcp/v1): Google returns HTTP 200 on initialize without auth, so OAuth never triggers and no tokens are stored. Proposed fix in fix(mcp): start OAuth when initialize succeeds without tokens langgenius/dify#36352 (discover OAuth metadata when tokens are absent, then initiate the flow). Confirms this is upstream Google behavior affecting multiple clients, not LibreChat-specific.

Workaround

Front the server with a sidecar (nginx/Caddy) that returns 401 for unauthenticated requests, forcing LibreChat into the OAuth flow.

Version / Environment

• LibreChat v0.8.6-rc1 (image registry.librechat.ai/danny-avila/librechat-dev:latest)
• librechat.yaml schema version 1.3.11
• Transport: streamable-http; server: Google hosted Drive MCP (https://drivemcp.googleapis.com/mcp/v1)
• Deployment: Docker Compose

[danny-avila]

Closed by #13254

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