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Proxy Authentication

This guide explains how to configure MCP Gateway to work with authentication proxies like OAuth2 Proxy, Authelia, Cloudflare Access, or enterprise API gateways.

Overview

When MCP Gateway is deployed behind an authentication proxy, you can disable its built-in JWT authentication and trust the proxy to handle user authentication. This is common in enterprise environments where authentication is centralized.

Architecture

User → Auth Proxy (OAuth/SAML) → MCP Gateway → MCP Servers
         ↓
    Identity Provider
    (Okta, Auth0, Azure AD)

Configuration

Environment Variables

To enable proxy authentication, configure these environment variables:

# Disable JWT authentication for MCP operations
MCP_CLIENT_AUTH_ENABLED=false

# REQUIRED: Explicitly trust proxy authentication
# Only set this when MCP Gateway is behind a trusted proxy!
TRUST_PROXY_AUTH=true

# Header containing the authenticated username from proxy
# Default: X-Authenticated-User
PROXY_USER_HEADER=X-Authenticated-User

# Keep admin UI authentication enabled (optional)
AUTH_REQUIRED=true

Security Warning

⚠️ IMPORTANT: Only disable MCP client authentication when MCP Gateway is deployed behind a trusted authentication proxy. Setting MCP_CLIENT_AUTH_ENABLED=false without TRUST_PROXY_AUTH=true will log a warning, as this removes a critical security layer.

Common Proxy Configurations

OAuth2 Proxy

OAuth2 Proxy is a popular reverse proxy that provides authentication using OAuth2 providers.

# docker-compose.yml
services:
  oauth2-proxy:
    image: quay.io/oauth2-proxy/oauth2-proxy:latest
    ports:
      - "4180:4180"
    environment:
      OAUTH2_PROXY_CLIENT_ID: your-client-id
      OAUTH2_PROXY_CLIENT_SECRET: your-client-secret
      OAUTH2_PROXY_COOKIE_SECRET: your-cookie-secret
      OAUTH2_PROXY_UPSTREAMS: http://mcp-gateway:4444
      OAUTH2_PROXY_PASS_USER_HEADERS: true
      OAUTH2_PROXY_SET_XAUTHREQUEST: true

  mcp-gateway:
    image: ghcr.io/contingentai/mcp-gateway:latest
    environment:
      MCP_CLIENT_AUTH_ENABLED: false
      TRUST_PROXY_AUTH: true
      PROXY_USER_HEADER: X-Auth-Request-User

Authelia

Authelia is a complete authentication and authorization server.

# Example Authelia forward auth configuration
services:
  authelia:
    image: authelia/authelia
    volumes:
      - ./authelia:/config
    environment:
      TZ: America/New_York

  mcp-gateway:
    image: ghcr.io/contingentai/mcp-gateway:latest
    environment:
      MCP_CLIENT_AUTH_ENABLED: false
      TRUST_PROXY_AUTH: true
      PROXY_USER_HEADER: Remote-User
    labels:
      - "traefik.http.routers.mcp.middlewares=authelia@docker"

Cloudflare Access

For Cloudflare Access, configure the gateway to read the authenticated user from Cloudflare's headers:

MCP_CLIENT_AUTH_ENABLED=false
TRUST_PROXY_AUTH=true
PROXY_USER_HEADER=Cf-Access-Authenticated-User-Email

AWS API Gateway

When using AWS API Gateway with Lambda authorizers:

MCP_CLIENT_AUTH_ENABLED=false
TRUST_PROXY_AUTH=true
PROXY_USER_HEADER=X-Authenticated-User

Configure your Lambda authorizer to add the authenticated username to the context:

# Lambda authorizer example
def lambda_handler(event, context):
    # Validate token...
    return {
        'principalId': user_id,
        'context': {
            'authenticatedUser': user_email
        }
    }

Header Passthrough

When using proxy authentication, you may want to pass additional headers to downstream MCP servers:

# Enable header passthrough
ENABLE_HEADER_PASSTHROUGH=true

# Headers to pass through (JSON array)
DEFAULT_PASSTHROUGH_HEADERS='["X-Tenant-Id", "X-Request-Id", "X-Authenticated-User"]'

Kubernetes with Istio

In a service mesh with Istio, you can use JWT validation at the mesh level:

apiVersion: security.istio.io/v1beta1
kind: RequestAuthentication
metadata:
  name: mcp-gateway-auth
spec:
  selector:
    matchLabels:
      app: mcp-gateway
  jwtRules:
  - issuer: "https://your-issuer.com"
    jwksUri: "https://your-issuer.com/.well-known/jwks.json"
---
apiVersion: v1
kind: ConfigMap
metadata:
  name: mcp-gateway-config
data:
  MCP_CLIENT_AUTH_ENABLED: "false"
  TRUST_PROXY_AUTH: "true"
  PROXY_USER_HEADER: "X-User-Id"

Testing Proxy Authentication

To test your proxy authentication setup:

  1. Without proxy headers (should fail or return anonymous): 

    curl http://localhost:4444/tools
# Returns 401 or anonymous access depending on AUTH_REQUIRED

  2. With proxy headers: 

    curl -H "X-Authenticated-User: john.doe@example.com" \
     http://localhost:4444/tools
# Should return tools list for authenticated user

  3. WebSocket with proxy auth: 

    const ws = new WebSocket('ws://localhost:4444/ws', {
  headers: {
    'X-Authenticated-User': 'john.doe@example.com'
  }
});

Troubleshooting

Warning: MCP auth disabled without trust

If you see this warning in logs: 

WARNING - MCP client authentication is disabled but trust_proxy_auth is not set

Solution: Set TRUST_PROXY_AUTH=true to acknowledge you're using proxy authentication.

Authentication still required

Problem: Getting 401 errors even with proxy headers.

Check: 1. Verify MCP_CLIENT_AUTH_ENABLED=false 2. Ensure TRUST_PROXY_AUTH=true 3. Confirm header name matches PROXY_USER_HEADER 4. Check proxy is actually sending the header

WebSocket connections fail

Problem: WebSocket connections are rejected.

Solution: Ensure your proxy passes headers to WebSocket upgrade requests. Some proxies require special configuration for WebSocket support.

Migration from JWT Authentication

To migrate from JWT to proxy authentication:

  1. Deploy proxy alongside existing setup
  2. Test proxy authentication with a subset of users
  3. Update environment: 
    MCP_CLIENT_AUTH_ENABLED=false
TRUST_PROXY_AUTH=true
PROXY_USER_HEADER=X-Authenticated-User
  4. Monitor logs for authentication issues
  5. Remove JWT token generation once stable

Security Best Practices

  1. Never expose MCP Gateway directly when proxy auth is enabled
  2. Use TLS between proxy and gateway
  3. Validate proxy certificates in production
  4. Monitor authentication logs for anomalies
  5. Implement rate limiting at the proxy level
  6. Use network policies to ensure only the proxy can reach the gateway

Example: Complete Setup with Traefik

# docker-compose.yml
version: '3.8'

services:
  traefik:
    image: traefik:v2.10
    command:
      - "--providers.docker=true"
      - "--entrypoints.web.address=:80"
    ports:
      - "80:80"
    volumes:
      - /var/run/docker.sock:/var/run/docker.sock

  oauth2-proxy:
    image: quay.io/oauth2-proxy/oauth2-proxy:latest
    environment:
      OAUTH2_PROXY_CLIENT_ID: ${CLIENT_ID}
      OAUTH2_PROXY_CLIENT_SECRET: ${CLIENT_SECRET}
      OAUTH2_PROXY_COOKIE_SECRET: ${COOKIE_SECRET}
      OAUTH2_PROXY_PROVIDER: google
      OAUTH2_PROXY_EMAIL_DOMAINS: "*"
      OAUTH2_PROXY_UPSTREAMS: "http://mcp-gateway:4444/"
      OAUTH2_PROXY_HTTP_ADDRESS: "0.0.0.0:4180"
      OAUTH2_PROXY_PASS_USER_HEADERS: "true"
      OAUTH2_PROXY_SET_XAUTHREQUEST: "true"
    labels:
      - "traefik.enable=true"
      - "traefik.http.routers.oauth2-proxy.rule=Host(`mcp.example.com`)"
      - "traefik.http.services.oauth2-proxy.loadbalancer.server.port=4180"

  mcp-gateway:
    image: ghcr.io/contingentai/mcp-gateway:latest
    environment:
      MCP_CLIENT_AUTH_ENABLED: "false"
      TRUST_PROXY_AUTH: "true"
      PROXY_USER_HEADER: "X-Auth-Request-Email"
      AUTH_REQUIRED: "true"  # Keep admin UI protected
      BASIC_AUTH_USER: ${ADMIN_USER}
      BASIC_AUTH_PASSWORD: ${ADMIN_PASSWORD}
    volumes:
      - ./data:/data

This configuration provides Google OAuth authentication for all MCP Gateway endpoints while maintaining separate admin UI authentication.