Working Twitter Application-Only OAuth2 RestSharp

string Authentication = EncodeTo64(ConsumerKey + ":" + ConsumerSecret);
RestClient twitterClient = new RestClient("https://api.twitter.com");
IRestResponse resp = null;
OAuthToken token = null;
RestRequest tweetReq = new RestRequest("oauth2/token", Method.POST);
tweetReq.AddHeader("Authorization", "Basic " + Authentication);
tweetReq.AddHeader("Host", "api.twitter.com");
tweetReq.AddHeader("User-Agent", "[APP NAME]");
tweetReq.AddHeader("Content-Type", "application/x-www-form-urlencoded;charset=UTF8");
tweetReq.AddParameter("grant_type", "client_credentials");
try
{
   resp = await twitterClient.GetResponseAsync(tweetReq);
   token = Newtonsoft.Json.JsonConvert.DeserializeObject<OAuthToken>(resp.Content);
}catch (Exception ex)
{
   // handle errors here
}

static public string EncodeTo64(string toEncode)
{
   byte[] toEncodeAsBytes
      = System.Text.UTF8Encoding.UTF8.GetBytes(toEncode);
   string returnValue
      = System.Convert.ToBase64String(toEncodeAsBytes);
   return returnValue;
}