public string GetPageContent(string url)
{
  string userName = null;
  SecureString password = null;
  var request = (HttpWebRequest)WebRequest.Create(url);
  var retry = true;
  var needAuth = false;
  while (retry)
  {
    try
    {
      if (needAuth && !string.IsNullOrWhiteSpace(userName))
      {
        request.Credentials = new NetworkCredential(userName, password ?? new SecureString());
      }

      var resp = (HttpWebResponse)request.GetResponse();
      using (var stream = resp.GetResponseStream())
      using (var reader = new StreamReader(stream))
      {
        return reader.ReadToEnd();
      }
    }
    catch (WebException e)
    {
      if (((HttpWebResponse)e.Response).StatusCode == HttpStatusCode.Unauthorized)
      {
        var args = new HttpExchangerNeedAuthEventArgs();
        if (NeedAuth != null)
        {
          NeedAuth.Invoke(this, args);
          if (args.Cancel)
            throw new WebException("Ошибка авторизаций");
          userName = args.UserName;
          password = args.Password;
        }
        else
          throw new WebException("Ошибка авторизаций");
        needAuth = true;
      }
      else
        throw new WebException("Ошибка авторизаций");
    }
  }
  throw new WebException("Ошибка авторизаций");
}