Proxy authentication details

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C#

dear everyone i made a windows application that connect to web service and get data from it.

many of my customers uses proxy to block the internet for users

all that i need to know is how to add proxy authentication details in my application to let the application connect to web service??

i want to show a form to add proxy details like this link (print screen)
i am using this code but i am still getting error and i can not connect to wen service

if (WebRequest.DefaultWebProxy.GetProxy(new System.Uri("https://www.o-survey.com/")).ToString() == "https://www.o-survey.com/")
            {
                MessageBox.Show("A proxy is not in use here");
            }
            else
            {
                MessageBox.Show("A proxy is in use here");
            }
 

HttpWebRequest request = (HttpWebRequest)WebRequest.Create("https://www.o-survey.com");

            IWebProxy proxy = request.Proxy;
            if (proxy != null)
            {
                MessageBox.Show("Proxy: {0}"+ proxy.GetProxy(request.RequestUri));
            }
            else
            {
                MessageBox.Show("Proxy: {0}Proxy is null; no proxy will be used");
            }

            WebProxy myProxy = new WebProxy();
            Uri newUri = new Uri("http://192.168.1.240:6588");
            // Associate the newUri object to 'myProxy' object so that new myProxy settings can be set.
            myProxy.Address = newUri;
            // Create a NetworkCredential object and associate it with the 
            // Proxy property of request object.
            myProxy.Credentials = new NetworkCredential("john", "johngra");
            request.Proxy = myProxy;

please advice as soon as possible