docs: def add_cors_headers(request, response):
      """Add cors headers needed for web app implementation."""
      response.headerlist.append(('Access-Control-Allow-Origin', '*'))
      response.headerlist.append(
          ('Access-Control-Allow-Methods', 'GET, OPTIONS'))
      response.headerlist.append(
          ('Access-Control-Allow-Headers',
           ','.join(DEFAULT_ACCESS_CONTROL_ALLOW_HEADERS)))