This MCP server can be configured to only accept connections from Anthropic's official IP addresses, providing an additional layer of security.

According to Anthropic's documentation, Claude uses these stable IP addresses for outbound MCP requests:

IPv4 Addresses:

• 34.162.46.92
• 34.162.102.82
• 34.162.136.91
• 34.162.142.92
• 34.162.183.95

To enable IP allowlisting in your deployment:

1. Import the security middleware in src/github-oauth-index.ts:

import { validateAnthropicOrigin, createSecurityHeaders } from './security-middleware';

2. Add validation to the SSE endpoint:

// In the SSE handler
if (url.pathname === '/sse') {
  // Validate request is from Anthropic
  if (!validateAnthropicOrigin(request)) {
    return new Response('Forbidden', { 
      status: 403,
      headers: createSecurityHeaders()
    });
  }
  // Continue with normal SSE handling...
}

3. Configure Cloudflare Firewall Rules (Optional but recommended):
   • Go to your Cloudflare dashboard
   • Navigate to Security > WAF > Custom rules
   • Create a new rule:
     • Field: IP Source Address
     • Operator: is not in
     • Value: 34.162.46.92, 34.162.102.82, 34.162.136.91, 34.162.142.92, 34.162.183.95
     • Path: equals /sse
     • Action: Block

Always validate that required secrets are present:

if (!env.LIMITLESS_API_KEY || !env.GITHUB_CLIENT_ID || !env.GITHUB_CLIENT_SECRET) {
  throw new Error('Missing required environment variables');
}

The security middleware includes rate limiting functionality. To enable it:

1. Create a KV namespace for rate limiting:

npx wrangler kv:namespace create "RATE_LIMIT_KV"

2. Add to your wrangler.toml:

[[kv_namespaces]]
binding = "RATE_LIMIT_KV"
id = "your-rate-limit-kv-id"

Consider implementing HMAC signing for MCP protocol messages:

function verifySignature(request: Request, secret: string): boolean {
  const signature = request.headers.get('X-MCP-Signature');
  const body = await request.text();
  const expectedSignature = await createHmacSignature(body, secret);
  return signature === expectedSignature;
}

Log security-relevant events:

interface SecurityEvent {
  timestamp: number;
  event: string;
  ip: string;
  userId?: string;
  details?: any;
}

async function logSecurityEvent(event: SecurityEvent, env: Env) {
  await env.AUDIT_KV.put(
    `audit:${Date.now()}:${crypto.randomUUID()}`,
    JSON.stringify(event),
    { expirationTtl: 2592000 } // 30 days
  );
}

• API Keys: Stored as encrypted Cloudflare secrets ✅
• OAuth Flow: Implements PKCE for authorization code flow ✅
• HTTPS Only: Enforced by Cloudflare Workers ✅
• Token Expiration: Short-lived tokens (1 hour) ✅
• State Validation: CSRF protection via state parameter ✅
• IP Allowlisting: Restrict to Anthropic IPs (optional)
• Rate Limiting: Configurable per-IP limits (optional)
• Security Headers: HSTS, CSP, X-Frame-Options (optional)
• Error Handling: Sanitized error messages
• Audit Logging: Track security events (optional)

1. Cloudflare Analytics: Monitor request patterns and anomalies
2. Workers Logs: Use wrangler tail to monitor live logs
3. KV Metrics: Track OAuth token usage and rate limit hits

If you suspect a security incident:

1. Immediately revoke the Limitless API key
2. Rotate GitHub OAuth credentials
3. Clear all KV namespaces:

   npx wrangler kv:key list --namespace-id=YOUR_OAUTH_KV_ID | \
   xargs -I {} npx wrangler kv:key delete {} --namespace-id=YOUR_OAUTH_KV_ID

4. Review Cloudflare logs for suspicious activity
5. Update IP allowlists if needed

Found a security vulnerability? Please report it by:

• Creating a private security advisory on GitHub
• Opening an issue at GitHub Issues

This security configuration is based on:

• Anthropic MCP documentation (January 2025)
• Cloudflare Workers best practices
• OAuth 2.0 Security Best Current Practice (RFC 8252)

Last updated: January 2025