HttpWebRequest timed out behind proxy

Hi,

I try to access web services behind a proxy. Until now, I used unitywebrequest but I understood that proxy configuration wasn't handled by them. So I changed my code to use HttpWebRequest as it allows manual proxy configuration.

I wrote a simple code to test this, but I'm still getting timeout.

         HttpWebRequest hwr = (HttpWebRequest)WebRequest.Create(ADMIN_URL);
 
         hwr.Method = "HEAD";
         hwr.Timeout = 5000;
         WebProxy proxy = new WebProxy(PROXY_URL, true);
         proxy.Credentials = new NetworkCredential(myLogin, myPassword);
         hwr.Proxy = proxy;        
 
         try
         {
             using (HttpWebResponse response = (HttpWebResponse)hwr.GetResponse())
             {
                 Debug.Log("response: " + response.StatusCode);             
             }
         }
         catch (Exception e)
         {            
             Debug.Log("Serveur not reachable: " + e.GetBaseException().Message);
         }

If I remove the proxy configuration (and use a connexion without proxy) it works. If i use the same code in a wpf .NET application (with proxy), it works.

I runned my tests through the Unity editor and with a pc standalone build.

My Unity version is 5.4.1f1

If you have any hint that can helps me... thank you