MCP OAuth — client_credentials grant ignored when CLIENT_SECRET is present

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1

I followed Model Context Protocol (MCP) | Cursor Docs to configure an MCP server using Client Credentials OAuth. Does Cursor support token generation using CLIENT_ID and CLIENT_SECRET in auth section of config and token_endpoint present in OAuth discovery response?

Where does the bug appear (feature/product)? - Cursor IDE

Summary

Cursor’s MCP client always uses the authorization code (redirect) flow when connecting to a URL-based MCP server, even when the MCP configuration includes CLIENT_SECRET. It does not use the client credentials grant to obtain an access token directly from the token_endpoint(present in OAuth discovery) using CLIENT_ID and CLIENT_SECRET.

Steps to reproduce

  1. Configure a URL-based MCP server in .cursor/mcp.json with:

    1. url: base URL of the MCP server (e.g. https://localhost:8000/mcp/app or a remote URL).
    2. auth containing:
      1. CLIENT_ID
      2. CLIENT_SECRET
      3. scopes (e.g. ["read","write"])

    Example (with placeholders):

    {
  "mcpServers": {
    "my-mcp": {
      "url": "https://localhost:8000/mcp/app",
      "auth": {
        "CLIENT_ID": "your_client_id",
        "CLIENT_SECRET": "your_client_secret",
        "scopes": ["read", "write"]
      }
    }
  }
}

  2. Ensure the MCP server (or its auth backend) serves /.well-known/oauth-authorization-server with:
    {
    "issuer":"``https://localhost:8000``",
    "authorization_endpoint":"``https://example.com/auth/api/authorize``", "token_endpoint":"``https://example.com/auth/api/token``", "response_types_supported":["code","token","id_token"], "token_endpoint_auth_methods_supported":["client_secret_basic"], "grant_types_supported":["client_credentials"]
    }

  3. In Cursor, add or reload the MCP server so it connects to the configured URL.

  4. Observe Cursor output/logs.

Result: Cursor prepares a redirect to the authorization endpoint and does not call the token endpoint with client credentials.

Expectation

When auth in mcp.json contains both CLIENT_ID and CLIENT_SECRET, and a token_endpoint is available (from the /.well-known/oauth-authorization-server discovery response), Cursor should:

  1. Use the client credentials grant (RFC 6749 §4.4).
  2. Request an access token by calling the token_endpoint with grant_type=client_credentials, authenticating with CLIENT_ID and CLIENT_SECRET (e.g. HTTP Basic or body parameters).
  3. Use the returned access token for MCP requests to the server.
  4. Not redirect the user to an authorization URL when a server-to-server credential is already configured.

Actual behavior

  1. Cursor fetches /.well-known/oauth-authorization-server from the MCP server URL.
  2. Cursor uses the authorization_endpoint from that discovery response to build an authorization (redirect) request, and logs that it is redirecting the user to the authorization URL.
  3. The token_endpoint from the discovery response is not used to obtain a token with CLIENT_ID and CLIENT_SECRET.
  4. Even with CLIENT_SECRET present in auth, Cursor still initiates the redirect-based flow (e.g. log message: “Redirect to authorization requested {“url”:"https://…….”).

Operating System - MacOS

Version Info:
Version: 2.5.17
VSCode Version: 1.105.1
Commit: 7b98dcb824ea96c9c62362a5e80dbf0d1aae4770
Date: 2026-02-17T05:58:33.110Z
Build Type: Stable
Release Track: Default
Electron: 39.3.0
Chromium: 142.0.7444.265
Node.js: 22.21.1
V8: 14.2.231.22-electron.0
OS: Darwin arm64 25.3.0

Does this stop you from using Cursor? - Sometimes - I can sometimes use Cursor

2

Hi there!

We detected that this may be a bug report, so we’ve moved your post to the Bug Reports category.

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