How to configure a app.config file in windows application with proxy settings, username and password

HttpWebRequest myWebRequest=(HttpWebRequest)WebRequest.Create("http://www.google.com");

    // Obtain the 'Proxy' of the  Default browser.  
    IWebProxy proxy = myWebRequest.Proxy;
    // Print the Proxy Url to the console.
    if (proxy != null)
    {
        Console.WriteLine("Proxy: {0}", proxy.GetProxy(myWebRequest.RequestUri));
    } 
    else
    {
        Console.WriteLine("Proxy is null; no proxy will be used");
    }