Claude.ai MCP Connector Failing to connect to my self-hosted n8n

Questions
1

I’m trying to connect Claude.ai to my self-hosted n8n via Instance-level MCP (OAuth). The OAuth flow appears to complete — I get redirected to n8n, I authorize, and n8n shows Claude as a Connected client. But Claude always returns “Authorization with the MCP server failed.”

I also tried creating a separate workflow with an MCP Server Trigger node (no auth) and using that Production URL as a custom connector in Claude. Same error.

My setup

  • n8n version: 2.12.3

  • Database: SQLite (default)

  • n8n EXECUTIONS_PROCESS setting: default

  • Running n8n via: npm (global install, Node.js v22.21.1 via nvm)

  • Operating system: macOS 14.2.1 (Apple Silicon)

n8n runs as a macOS LaunchAgent and is exposed to the internet via Cloudflare Tunnel (cloudflared 2025.11.1) routing n8n.jeffzeb.com → http://127.0.0.1:5678.

What I’ve tried

  • Confirmed endpoint is reachable: curl -I returns HTTP 401 with Bearer auth as expected

  • Added N8N_PROXY_HOPS=1 and N8N_TRUST_PROXY=true (fixed an ERR_ERL_UNEXPECTED_X_FORWARDED_FOR error in the MCP SDK)

  • Created a Cloudflare Transform Rule to set Origin: https://n8n.jeffzeb.com (known issue with tunnels stripping the scheme)

  • Revoked old Connected clients and re-added the connector fresh

  • Tested in both Safari and Chrome

  • Tested both Instance-level MCP (OAuth) and MCP Server Trigger (no auth) — both fail with the same error

  • Workflows are enabled for MCP access and active

Key observation

OAuth completes on n8n’s side (Connected clients tab confirms it), but Claude doesn’t recognize the connection as successful. This happens with both the instance-level MCP URL and a standalone MCP Server Trigger URL.

Has anyone successfully connected Claude.ai (not Claude Desktop) to a self-hosted n8n behind a Cloudflare Tunnel? Any ideas what could be failing after the OAuth callback? Also possible issue is on the Claude side, so I’ve reached out to their help support as well.

2

Hi @GeoffS , welcome to the n8n community :tada:

What stands out to me is that both the OAuth connector and the no-auth MCP Server Trigger fail the same way, so I’d be cautious about blaming OAuth itself, to me that points more toward a reverse-proxy / transport issue after the callback, especially since n8n behind a proxy needs the original forwarded host/proto headers and usually a fixed WEBHOOK_URL, plus Cloudflare can sometimes interfere with streaming/compression behavior.

could you please share the response headers and body you get from the MCP endpoint with curl -i, and whether Cloudflare has compression, caching, Access, or any other edge features enabled on that hostname/path?

4

Cloudflare Tunnel buffers streaming responses by default, which breaks the MCP transport even though the OAuth redirect works fine. Add disableChunkedEncoding: true to your cloudflared config for that ingress rule. Also make sure WebSockets are enabled in the Cloudflare dashboard under Network for your domain.

6

Thanks everyone for the quick responses! Here’s what I found after working through them:

@pvdyck

disableChunkedEncoding: true Added this to my cloudflared config and restarted the tunnel. This was a good call and may have fixed the streaming issue, but the auth error persists.

@tamy.santos

Here’s what curl -i shows for the instance-level MCP endpoint:

  • GET returns HTTP 200 with the n8n editor HTML (falls through to frontend)

  • POST with MCP initialize payload returns: {"message":"Unauthorized: Authorization header not sent"}— so the endpoint is alive and correctly requiring auth

For the MCP Server Trigger endpoint (no auth), POST with MCP initialize returns a proper response:

event: message
data: {"result":{"protocolVersion":"2024-11-05","capabilities":{"tools":{}},"serverInfo":{"name":"MCP_Server_Trigger","version":"0.1.0"},"jsonrpc":"2.0","id":1}

Response headers include content-type: text/html; charset=utf-8, access-control-allow-origin: ``https://n8n.xxxxxxxx.com, cache-control: no-cache, no-store, cf-cache-status: DYNAMIC. No compression or caching issues visible.

BenB

As shown above, the MCP Server Trigger returns a valid initialize response with correct tools capability and protocol version. Transport is working fine — the disableChunkedEncoding fix plus WebSockets enabled in Cloudflare means streaming isn’t being buffered.

Both endpoints work correctly at the transport level when tested with curl. The OAuth flow also completes — n8n shows Claude as a Connected client after I authorize. But Claude.ai still returns “Authorization with the MCP server failed” every time.

Even the no-auth MCP Server Trigger fails with the same error, which suggests Claude.ai’s custom connector is attempting OAuth regardless and something in that exchange isn’t completing on Claude’s side.

I also fixed an ERR_ERL_UNEXPECTED_X_FORWARDED_FOR error earlier by adding N8N_TRUST_PROXY=true — the error log is clean now.

Has anyone gotten Claude.ai (not Claude Desktop) working with a self-hosted n8n behind Cloudflare Tunnel specifically? Starting to wonder if this is a Claude-side issue with the OAuth callback.

7

Also, @tamy.santos here’s what you asked for.

curl -i against the instance-level MCP endpoint (POST):

HTTP/2 401
content-type: application/json; charset=utf-8
content-length: 57
access-control-allow-credentials: true
access-control-allow-headers: Origin, X-Requested-With, Content-Type, Accept, push-ref, browser-id, anonymousid, authorization, x-authorization
access-control-allow-methods: GET, POST, OPTIONS, PUT, PATCH, DELETE
access-control-allow-origin: https://n8n.xxxxxxx.com
etag: W/"39-2hSNeRgbNg6crq17Q/2hLPX4gMU"
vary: Accept-Encoding
www-authenticate: Bearer realm="n8n MCP Server"
cf-cache-status: DYNAMIC

{"message":"Unauthorized: Authorization header not sent"}

curl -i against the MCP Server Trigger endpoint (no auth, POST):

HTTP/2 200
content-type: text/event-stream
content-length: 178
access-control-allow-methods: OPTIONS, DELETE, GET, POST
access-control-allow-origin: https://n8n.xxxxxxx.com
cache-control: no-cache
mcp-session-id: 9bcea911-251c-4dd2-ab03-d8c28c93fc9a
vary: Accept-Encoding
cf-cache-status: DYNAMIC

event: message
data: {"result":{"protocolVersion":"2024-11-05","capabilities":{"tools":{}},"serverInfo":{"name":"MCP_Server_Trigger","version":"0.1.0"},"jsonrpc":"2.0","id":1}

Cloudflare edge features:

  • No custom caching, compression, or Access policies on this hostname

  • WebSockets enabled

  • One active rule: Modify Request Header setting Origin: https://n8n.xxxxxxx.com

  • Tunnel config has disableChunkedEncoding: true per @pvdyck’s suggestion

11

@GeoffS Si tu es ouvert à l’utilisation de Claude Desktop ou Claude Code CLI au lieu de Claude.ai web, il existe une approche qui évite complètement le problème OAuth. J’ai créé un serveur MCP Python qui se connecte via stdio en utilisant directement l’API REST de n8n ; pas de complications de tunneling Cloudflare, pas de handshake OAuth. Ça vaut peut-être le coup d’essayer : https://github.com/DerJams/n8n-mcp-server-python

12

merci pour les informations @GeoffS

donc, j’ai le regret de te dire mais il semble que le problème soit la différence entre Claude Desktop et Claude AI. La doc parle du déclencheur MCP en référence à Claude Desktop uniquement, je n’ai rien trouvé sur le connecteur personnalisé Claude.ai, et le fait que le endpoint sans authentification échoue avec la même erreur suggère qu’il peut appliquer son propre flux d’autorisation ou ne pas accepter ce type de endpoint. Le workaround pratique serait de tester avec Claude Desktop ou un autre MCP supporté/documenté. Si Claude.ai est obligatoire, j’utiliserais temporairement un proxy/adaptateur entre Claude.ai et n8n.

voici les docs pour soutenir
MCP connector - Claude API Docs
MCP Server Trigger node documentation | n8n Docs
Set up and use n8n MCP server | n8n Docs

13

Merci @tamy.santos. J’avais mis ce projet de côté depuis un moment, mais je vais le revoir avec ta documentation. Malheureusement, je n’ai pas eu plus de chance avec Claude Desktop non plus.

14

zut :frowning:
quel dommage.

16

Mise à jour : ça marche !

Le flux du connecteur OAuth ne fonctionne toujours pas — il y a apparemment un bug du côté de Claude où il complète la poignée de main OAuth mais n’attache jamais le jeton Bearer aux demandes MCP suivantes. Je l’ai signalé au support Anthropic et ils l’ont reconnu comme un problème connu.

Ce qui a marché : contourner complètement OAuth en utilisant le fichier de configuration de Claude Desktop avec un jeton Bearer.

  1. Récupérez votre Access Token depuis n8n Settings → Instance-level MCP → Connection details → onglet Access Token

  2. Modifiez ~/Library/Application Support/Claude/claude_desktop_config.json

  3. Ajoutez un bloc mcpServers :

{
  "mcpServers": {
    "n8n": {
      "command": "npx",
      "args": [
        "-y",
        "mcp-remote",
        "https://your-n8n-domain.com/mcp-server/http",
        "--header",
        "Authorization: Bearer YOUR_ACCESS_TOKEN_HERE"
      ]
    }
  }
}
  1. Redémarrez Claude Desktop

Cela utilise mcp-remote pour faire un pont entre le transport stdio de Claude Desktop et le point de terminaison HTTP de n8n avec le jeton passé directement. Pas besoin de poignée de main OAuth.

Remarque : cela ne fonctionne que dans Claude Desktop, pas sur claude.ai dans le navigateur. Le jeton peut également expirer, vous devrez donc probablement le rafraîchir périodiquement.

Autres correctifs qui ont été nécessaires en chemin (si vous exécutez n8n derrière un Cloudflare Tunnel) :

  • disableChunkedEncoding: true dans la config cloudflared (prévient la mise en buffer SSE)

  • Variable d’environnement N8N_TRUST_PROXY=true (corrige ERR_ERL_UNEXPECTED_X_FORWARDED_FOR dans le SDK MCP)

  • Règle Cloudflare Transform pour définir Origin: https://your-domain.com (corrige le problème de suppression de schéma)

  • WebSockets activés dans les paramètres Cloudflare Network

Merci @tamy.santos, BenB, pvdyck, unstableentity et @syed_noor pour toute l’aide apportée pour affiner cela.

17

Super discussion ! Une chose à noter :

Les serveurs MCP fonctionnent mieux avec le transport stdio

pour les configurations Claude Desktop locales, et SSE

pour les déploiements distants/serveur.

J’exécute un serveur MCP Flowmatic personnalisé

reliant Claude aux données de marché en direct

et à la gestion de portefeuille — je serais heureux de partager

l’architecture si cela peut être utile.