var credentialStringValue = "proxyUser:proxyPassword";
byte[] credentialByteArray = ASCIIEncoding.ASCII.GetBytes(credentialStringValue);
var credentialBase64String = Convert.ToBase64String(credentialByteArray);

string Headers = string.Format("Proxy-Authorization: Basic {0}{1}", credentialBase64String, Environment.NewLine);

ws.Navigate(url,TargetFrameName,PostData,Headers);

// do what you want with proxy class
WebProxy webProxy = new WebProxy(host, port)
{
    Credentials = ...
}

HttpWebRequest webRequest = (HttpWebRequest)WebRequest.Create("http://example.com");
webRequest.Proxy = webProxy;

HttpWebResponse response = (HttpWebResponse)webRequest.GetResponse();
Stream receiveStream = response.GetResponseStream();

WebBrowser webBrowser = new WebBrowser();
webBrowser.DocumentStream = receiveStream;

Registry.SetValue(keyName, "ProxyServer", proxyhost, RegistryValueKind.String);
        Registry.SetValue(keyName, "ProxyEnable", proxyEnabled ? "1" : "0", RegistryValueKind.DWord);

        Registry.SetValue(keyName, "ProxyPass", password, RegistryValueKind.String);
        Registry.SetValue(keyName, "ProxyUser", username, RegistryValueKind.String);

        //<-loopback>;<local>
        Registry.SetValue(keyName, "ProxyOverride", "*.local", RegistryValueKind.String);


        // These lines implement the Interface in the beginning of program
        // They cause the OS to refresh the settings, causing IP to realy update
        InternetSetOption(IntPtr.Zero, INTERNET_OPTION_SETTINGS_CHANGED, IntPtr.Zero, 0);
        InternetSetOption(IntPtr.Zero, INTERNET_OPTION_REFRESH, IntPtr.Zero, 0);
    }

Credential credentials= new Credential
            {
                Username = $"Usernmae",
                Password = "Password",
                Target = "Target (usualy proxy domain}",
                Type = CredentialType.Generic,
                PersistanceType = PersistanceType.Enterprise
            };
            credentials.Save();