Problema com autenticação OAuth no MCP Server / OAuth Authentication Failing with MCP Server

[Rogerio_Assis]

English Version:
Dear all,

I’m trying to use the MCP Server (GitHub - takumi0706/google-calendar-mcp: Google Calendar MCP server for Claude Desktop integration) in n8n. The installation was successful, but I’m unable to complete the OAuth authentication.

The credentials work fine when I use the standard Google Calendar node in n8n.

For the MCP Server, I used the following configuration:

• Command: npx
• Arguments: -y @takumi0706/google-calendar-mcp
• Environment Variables:
  • GOOGLE_CLIENT_ID=MY_CLIENT_ID
  • GOOGLE_CLIENT_SECRET=MY_CLIENT_SECRET
  • GOOGLE_REDIRECT_URI=https://n8n.meun8n.com.br/rest/oauth2-credential/callback

I also tried the following callback URLs without success:

• http://localhost:3000/oauth2callback
• urn:ietf:oauth:2.0:oob

Could anyone shed some light on this issue?

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Versão em Português (PT-BR):
Prezados,

Estou tentando usar o MCP Server (GitHub - takumi0706/google-calendar-mcp: Google Calendar MCP server for Claude Desktop integration) no n8n. A instalação foi concluída com sucesso, mas não consigo completar a autenticação OAuth.

As credenciais funcionam normalmente quando uso o node padrão do Google Calendar no n8n.

No MCP Server, utilizei a seguinte configuração:

• Comando: npx
• Argumentos: -y @takumi0706/google-calendar-mcp
• Variáveis de Ambiente:
  • GOOGLE_CLIENT_ID=MEU_CLIENT_ID
  • GOOGLE_CLIENT_SECRET=MEU_CLIENT_SECRET
  • GOOGLE_REDIRECT_URI=https://n8n.meun8n.com.br/rest/oauth2-credential/callback

Também tentei as seguintes URLs de callback, sem sucesso:

• http://localhost:3000/oauth2callback
• urn:ietf:oauth:2.0:oob

Alguém poderia me ajudar com esse problema?

[jcuypers]

Hi, if you try to create manual OAuth2 credentials for some server in n8n, what is the host and port proposed by the software. You should use these in the environment variable. Most likely you didn’t use the correct port or hosr

[Rogerio_Assis]

English Version:

Thanks for your suggestion! I’ve already tried the following callback URLs without success:

1. http://localhost:5678/rest/oauth2-credential/callback (n8n’s default port)
2. https://n8n.meun8n.com.br/rest/oauth2-credential/callback (public URL)
3. http://localhost:3000/oauth2callback (common alternative)
4. urn:ietf:wg:oauth:2.0:oob (out-of-band mode)

The credentials work perfectly with n8n’s native Google Calendar node, but fail with the MCP Server. Could you clarify:

• Are there specific scopes required for the MCP Server?
• Should the GOOGLE_REDIRECT_URI match exactly the authorized URI in Google Cloud Console?
• Is there a debugging step (e.g., logs) to identify where the handshake fails?

I’d appreciate any details to narrow this down!

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Versão em Português (PT-BR):

Agradeço pela sugestão! Já tentei as seguintes URLs de callback sem sucesso:

1. http://localhost:5678/rest/oauth2-credential/callback (porta padrão do n8n)
2. https://n8n.meun8n.com.br/rest/oauth2-credential/callback (URL pública)
3. http://localhost:3000/oauth2callback (alternativa comum)
4. urn:ietf:wg:oauth:2.0:oob (modo “out-of-band”)

As credenciais funcionam perfeitamente com o node nativo do Google Calendar no n8n, mas falham com o MCP Server. Poderia detalhar:

• Há scopes específicos obrigatórios para o MCP Server?
• O GOOGLE_REDIRECT_URI deve ser idêntico ao URI autorizado no Google Cloud Console?
• Existe alguma etapa de debug (ex.: logs) para identificar onde o handshake falha?

Ajudaria muito ter mais informações para resolver isso!

[takumi0706]

Hello, I am the author of this repository.
I think this is due to the authentication server having a different port.

If you change the port number for “GOOGLE_REDIRECT_URI” from “3000” to “4153”, you will be able to clear OAuth.

Also,

@Rogerio_Assis

Should the GOOGLE_REDIRECT_URI match exactly the authorized URI in Google Cloud Console?

This is Yes.

@Rogerio_Assis

Is there a **debugging step** (e.g., logs) to identify where the handshake fails?

If you are running it on the console, the information should appear on the console, and if you are running it on the MCP client, it should appear in the client log.