ClickUp OAuth Integration with n8n via Docker/Traefik Fails with "Unsupported content type: text/html

Questions
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1

Problem Description

I’m unable to connect ClickUp via OAuth in my self-hosted n8n instance (tag:latest). The setup uses Docker Compose with Traefik: s a reverse proxy and n8n’s
During OAuth authentication:

  1. I enter the generated callback URL in ClickUp’s node:
    https://n8n.domain.com/rest/oauth2-credential/callback **
    in clickup GUI it is being truncated to only domain part - n8n.domain.com without full path**

  2. ClickUp’s authorization dialog appears, but after granting access to workspace, I get:

Error: Unsupported content type: text/html Failed to connect. The window can be closed now.

  1. Traefik logs show no errors, but n8n logs indicate the callback returns HTML instead of expected JSON. Also same in DevTools preview in Chrome

Suspected Issue:

  • Traefik middleware might be modifying headers/responses.
  • ClickUp expects strict application/json but receives HTML (possibly a fallback error page).

My Environment

  • OS: Ubuntu 22.04 LTS
  • Docker: 24.0.7
  • Tools:
    • Traefik v2.10.7 (reverse proxy with Let’s Encrypt)
    • n8n:latest

Configuration Files

docker-compose.yml

services:
  traefik:
    image: "traefik"
    restart: always
    command:
      - "--api.insecure=true"
      - "--providers.docker=true"
      - "--providers.docker.exposedbydefault=false"
      - "--entrypoints.web.address=:80"
      - "--entrypoints.web.http.redirections.entryPoint.to=websecure"
      - "--entrypoints.web.http.redirections.entrypoint.scheme=https"
      - "--entrypoints.websecure.address=:443"
      - "--certificatesresolvers.mytlschallenge.acme.tlschallenge=true"
      - "--certificatesresolvers.mytlschallenge.acme.email=${SSL_EMAIL}"
      - "--certificatesresolvers.mytlschallenge.acme.storage=/letsencrypt/acme.json"
      - "--log.level=DEBUG"
    ports:
      - "80:80"
      - "443:443"
    volumes:
      - traefik_data:/letsencrypt
      - /var/run/docker.sock:/var/run/docker.sock:ro

  n8n:
    image: docker.n8n.io/n8nio/n8n
    restart: always
    ports:
      - "127.0.0.1:5678:5678"
    labels:
      - traefik.enable=true
      - traefik.http.routers.n8n.rule=Host(`${SUBDOMAIN}.${DOMAIN_NAME}`)
      - traefik.http.routers.n8n.tls=true
      - traefik.http.routers.n8n.entrypoints=web,websecure
      - traefik.http.routers.n8n.tls.certresolver=mytlschallenge
      - traefik.http.middlewares.n8n.headers.SSLRedirect=true
      - traefik.http.middlewares.n8n.headers.STSSeconds=315360000
      - traefik.http.middlewares.n8n.headers.browserXSSFilter=true
      - traefik.http.middlewares.n8n.headers.contentTypeNosniff=true
      - traefik.http.middlewares.n8n.headers.forceSTSHeader=true
      - traefik.http.middlewares.n8n.headers.SSLHost=${DOMAIN_NAME}
      - traefik.http.middlewares.n8n.headers.STSIncludeSubdomains=true
      - traefik.http.middlewares.n8n.headers.STSPreload=true
      - traefik.http.routers.n8n.middlewares=n8n-headers@docker
      - traefik.http.middlewares.n8n-headers.headers.customrequestheaders.X-Forwarded-Proto=https
      - traefik.http.middlewares.n8n-headers.headers.customrequestheaders.X-Forwarded-Host=n8n.blagohod.ru    
      - traefik.http.middlewares.n8n-headers.headers.customrequestheaders.Host=n8n.blagohod.ru
    environment:
      - N8N_HOST=https://${SUBDOMAIN}.${DOMAIN_NAME}
      - N8N_PORT=5678
      - N8N_PROTOCOL=https
      - NODE_ENV=production
      - WEBHOOK_URL=https:///${SUBDOMAIN}.${DOMAIN_NAME}/
      - GENERIC_TIMEZONE=${GENERIC_TIMEZONE}
      - N8N_LOG_LEVEL=debug
    volumes:
      - n8n_data:/home/node/.n8n
      - ./local-files:/files

volumes:
  n8n_data:
  traefik_data:

Steps I Tried

  1. Verified ClickUp OAuth Settings:
    Current vaules:
    n8n.domain.com
    n8n.domain.com:5678

Changed vars in env for n8n image
WEBHOOK_URL=https:///${SUBDOMAIN}.${DOMAIN_NAME}/ + PORT and without port

  1. Adjusted Traefik Middleware:
  • Added headers to enforce Content-Type: application/json:

command: - “–experimental.http.middlewares.n8n-headers.headers.customResponseHeaders.Content-Type=application/json”

  • Disabled compression:
  • “–experimental.http.middlewares.n8n-no-compress.compress=false”
  1. n8n Environment Variables:

environment: - N8N_PROXY_CORS=true - N8N_DISABLE_PRODUCTION_MAIN_PAGE=true

Key Questions

  1. How can I configure Traefik to not interfere with n8n’s OAuth callbacks?
  2. Are there specific headers/middleware needed for ClickUp’s OAuth?
  3. Why does the callback return HTML instead of JSON when behind Traefik?

Any debugging tips or working Traefik+n8n examples would be appreciated!