How can we use proxy for websockets?

url1, err := url.Parse("http://dummy.com") // proxy url
fmt.Println(url1, err)
fialer := websocket.DefaultDialer
fialer.Proxy = transport.ProxyURL(url1)

con, res, err := fialer.Dial(m.wsEndpoint, nil)
if err != nil {
fmt.Println(err, "====================================", res)
return err
}

this is giving **Proxy Authentication Required** error.