Hi all,
I am trying to connect the built-in Home Assistant MCP Server to ChatGPT as a custom MCP connector via Nabu Casa.
Home Assistant Core is up to date.
I tested both MCP endpoints:
https://<redacted>.ui.nabu.casa/api/mcp
https://<redacted>.ui.nabu.casa/api/mcp/assist
During connector creation in ChatGPT, OAuth fails before the Home Assistant login/authorization flow starts.
ChatGPT shows this error:
OAuth authorization server metadata must advertise PKCE support with code_challenge_methods_supported containing S256.
I checked the OAuth authorization server metadata at:
https://<redacted>.ui.nabu.casa/.well-known/oauth-authorization-server
The response is:
"authorization_endpoint": "https://<redacted>.ui.nabu.casa/auth/authorize",
"token_endpoint": "https://<redacted>.ui.nabu.casa/auth/token",
"revocation_endpoint": "https://<redacted>.ui.nabu.casa/auth/revoke",
"client_id_metadata_document_supported": true,
"response_types_supported": [
"code"
],
"service_documentation": "https://developers.home-assistant.io/docs/auth_api",
"issuer": "https://<redacted>.ui.nabu.casa"
}
However, the metadata does not include:
{ "code_challenge_methods_supported": [ "S256" ] }`
This seems to be the reason why ChatGPT refuses to create the connector.
Steps I tried:
1. Removed and re-added the Home Assistant MCP Server integration.
2. Tried /api/mcp.
3. Tried /api/mcp/assist.
4. Tried OAuth authentication.
5. Tried mixed authentication.
6. Reconnected the ChatGPT custom MCP connector.
7. Confirmed that Home Assistant Core is up to date.
Expected result:
ChatGPT should be able to create the custom MCP connector and start the OAuth authorization flow against Home Assistant.
Actual result:
ChatGPT refuses to create the connector because the OAuth metadata does not advertise PKCE S256 support.
Is this a known limitation or bug in the current Home Assistant MCP/OAuth metadata endpoint, especially when using Nabu Casa? It did work fine before.
Thanks!