How to retrieve Token from WebApi

For 2 days I have been looking how to connect and perform queries in a web api, but it still did not work.. I need help, someone here can give me some example how i can connect to my webapi from C# Winforms. See below for some information:

Server for authentication: http://ift.tt/2sJrufO grant_type="client_credentials"
clientId="property-search-web-site"
clientSecret="999999999"
tenant="XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX"
post / x-www-form-urlencoded

Someone have example or can help fix my code:

public class Token
    {
        [JsonProperty("access_token")]
        public string AccessToken { get; set; }
        [JsonProperty("token_type")]
        public string TokenType { get; set; }
        [JsonProperty("expires_in")]
        public int ExpiresIn { get; set; }
        [JsonProperty("refresh_token")]
        public string RefreshToken { get; set; }
        [JsonProperty("error")]
        public string Error { get; set; }
    }

    public static string GenerateApiKey()
    {

        var appSettings = ConfigurationManager.AppSettings;
        try
        {
            string tenant = "XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX";

            var urlToCall = string.Format("http://ift.tt/2sJrufO" + tenant + "/oauth/token");

            var uri = new Uri(urlToCall);

            var request = (HttpWebRequest)WebRequest.Create(uri);
            request.Method = "POST";

            var postItems = new List<KeyValuePair<string, string>>
            {
                new KeyValuePair<string, string>("grant_type", "client_credentials"),
                new KeyValuePair<string, string>("client_id", "property-search-web-site"),
                new KeyValuePair<string, string>("client_secret", "999999999"),
            };

            string postData = string.Join("&",
                postItems.Select(kvp =>
                   string.Format("{0}={1}", kvp.Key, HttpUtility.UrlEncode(kvp.Value))));

            byte[] byteArray = Encoding.UTF8.GetBytes(postData);
            ServicePointManager.Expect100Continue = false;
            request.ContentType = "application/x-www-form-urlencoded";
            request.ContentLength = byteArray.Length;

            Stream dataStream = request.GetRequestStream();
            dataStream.Write(byteArray, 0, byteArray.Length);
            dataStream.Close();

            ServicePointManager.Expect100Continue = false;
            var response = (HttpWebResponse)request.GetResponse();



            using (StreamReader sr = new StreamReader(response.GetResponseStream()))
            {

            }

            return "";
        }
        catch (Exception e)
        {
            throw new Exception("Error getting a response from API  " + e.Message);
        }
    }