code: def is_cross_origin(request):
      
      origin = request.environ.get("HTTP_ORIGIN")
      host = request.environ.get("HTTP_HOST")
      if origin is None:
          # origin is sometimes omitted by the browser when origin and host are equal
          return False
  
      if origin.startswith("http://"):
          origin = origin.replace("http://", "")
      elif origin.startswith("https://"):
          origin = origin.replace("https://", "")
      return host != origin
docs: Compare headers HOST and ORIGIN. Remove protocol prefix from ORIGIN, then
      compare. Return true if they are not equal
      example HTTP_HOST: '127.0.0.1:5000'
      example HTTP_ORIGIN: 'http://127.0.0.1:5000'