Cloudflare reverse proxy via workers - generated by ChatGPT

gistfile1.js

export default {
  async fetch(request, env, ctx) {
    return handleRequest(request)
  }
}

async function handleRequest(request) {
  const url = new URL(request.url)

  if (url.pathname.startsWith('/app2/')) {
    url.hostname = 'server2.example.com'
    url.protocol = 'https'
    url.port = ''

    const newHeaders = new Headers(request.headers)
    newHeaders.set('Host', request.headers.get('Host'))  // Equivalent to proxy_set_header Host $host
    newHeaders.set('X-Real-IP', request.headers.get('CF-Connecting-IP') || request.headers.get('X-Real-IP'))
    newHeaders.set('X-Forwarded-For', request.headers.get('CF-Connecting-IP') || request.headers.get('X-Forwarded-For'))
    newHeaders.set('X-Forwarded-Proto', request.headers.get('X-Forwarded-Proto') || url.protocol)

    const newRequest = new Request('https://the-other-server.example.com', {
      method: request.method,
      headers: newHeaders,
      body: request.body,
      redirect: 'manual'
    })

    const response = await fetch(newRequest)
    return response
  }

  return fetch(request)
}