authentication - Go http proxy with auth

Question

I need to use a proxy with auth using PostForm method. If I use something like (simplified):

request, err := http.NewRequest("GET", url.String(), nil)
response, err := client.Do(request)

I can with ease do request.Header.Add("Proxy-Authorization", basicAuth) and it works fine. But now, I am editing third-party package, and I try to add proxy to the existing code:

    proxyStr := "http://proxy.com:8080"
    proxyURL, _ := url.Parse(proxyStr)

    transport := &http.Transport{
        Proxy: http.ProxyURL(proxyURL),
    }
    bot.Client = &http.Client{
        Transport: transport,
    }

    resp, err := bot.Client.PostForm(method, params)

    auth := "username:password"
    basicAuth := "Basic " + base64.StdEncoding.EncodeToString([]byte(auth)) 
    resp.Header.Add("Proxy-Authorization", basicAuth)

It does not work, and it fails, to my mind, at string resp.Header.Add("Proxy-Authorization", basicAuth). Proxy without auth works fine, in this example. Does anybody know, can I use proxy with auth in this case?

Answer 1

Waitting for answers