MainWindow main = new MainWindow();

var client_id = 123456;
var client_secret = "qwerty";
var AudioBotVk = new HttpClient();
//WebProxy webProxy = new WebProxy(main.ProxyBox.ToString(), true);

HttpWebRequest request = (HttpWebRequest)WebRequest.Create(
    "https://oauth.vk.com/token?scope=nohttps%2Call&client_id="
    + client_id + "&client_secret=" + client_secret
    + "&2fa_supported=1&lang=ru&grant_type=password&username="
    + main.LoginBox.Text.ToString() + "&password=" + main.PasswordBox.ToString()
    + "&libverify_support=1");

request.Method = "GET";
request.Host = "oauth.vk.com";
request.UserAgent = "Foo/bar (param1; param2; param3; param4; ru)";
request.ContentType = "application/x-www-form-urlencoded";


HttpWebResponse responsevk = (HttpWebResponse)request.GetResponse();

int appID = 12345;                      // ID приложения
string email = "test@test.com";         // email или телефон
string pass = "password";               // пароль для авторизации
Settings scope = Settings.Friends;      // Приложение имеет доступ кдрузьям

var vk = new VkApi();
vk.Authorize(new ApiAuthParams)
{
  ApplicationId = (ulong)appID,
  Login = email,
  Password = pass,
  Settings = scope
};

public static void VkAuth1()
    {
        var login = "логин";
        var password = "пароль";

        var AudioBotVk = new HttpClient();
        AudioBotVk.DefaultRequestHeaders.Add("Connection", "close");

        string url = string.Format("https://oauth.vk.com/token?scope=nohttps%2Call
&client_id=123456&client_secret=qwertyu&2fa_supported=1&lang=ru
&device_id=123456789def&grant_type=password&username={0}&password={1}&libverify_support=1",
login, password);


        HttpWebRequest request = (HttpWebRequest)WebRequest.Create(url);
        request.Method = "GET";
        request.Host = "oauth.vk.com";
        request.UserAgent = "qwert";
        request.ContentType = "application/x-www-form-urlencoded";
        request.KeepAlive = false;

        using (HttpWebResponse responsevk = (HttpWebResponse)request.GetResponse())
        using (var stream = responsevk.GetResponseStream())
        using (var streamReader = new StreamReader(stream, Encoding.UTF8))
        {

            Debug.WriteLine(streamReader.ReadToEnd());

        }

        Console.ReadLine();
    }