Codex Notion OAuth fails with invalid_target: duplicate resource parameters

Codex Bugs
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1

Environment

  • Surface: Codex desktop app
  • OS/browser: macOS / Chrome
  • Integration: Notion MCP (https://mcp.notion.com/mcp)
  • Observed: October 13, 2026 (America/Los_Angeles)

Bug

While connecting Notion, the OAuth authorization URL contained two resource query parameters. Opening it returned:

{"error":"invalid_target","error_description":"Only one resource parameter is supported."}

I expected the authorization flow to proceed to Notion sign-in/consent. Instead, this error blocked the connection.

Reproduction / URL details

The authorization endpoint was https://mcp.notion.com/authorize, with the Codex client ID https://chatgpt.com/oauth/codex/client.json and both of these parameters (decoded for readability):

resource=https://mcp.notion.com/mcp
resource=https://mcp.notion.com

The request also used response_type=code, code_challenge_method=S256, scope=default, and a localhost callback. Session-specific state, PKCE challenge, and callback port are omitted here.

Suggested investigation

Please check why both resource values are included in the Notion authorization request. The Notion endpoint explicitly rejects multiple resource parameters. A proposed workaround is to remove resource=https://mcp.notion.com and retain only resource=https://mcp.notion.com/mcp; I have not yet confirmed the end-to-end result of that workaround.

Is this a known issue with the Codex Notion OAuth flow?

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