public static async Task<Uri> CrearitemAsync(Item item)
{
client.BaseAddress = new Uri(BaseUri);
client.DefaultRequestHeaders.Accept.Clear();
client.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("OAuth", AuthToken);
HttpResponseMessage response = await client.PostAsJsonAsync("items/" + IdProvider, JsonConvert.SerializeObject(item));
response.EnsureSuccessStatusCode();
return response.Headers.Location;
}

var httpWebRequest = (HttpWebRequest)WebRequest.Create("http://ejemplo.com/items/id");
        httpWebRequest.PreAuthenticate = true;
        httpWebRequest.Headers.Add("Authorization", "Bearer " + AuthToken);
        httpWebRequest.ContentType = "application/json";
        httpWebRequest.Method = "POST";
        using (var streamWriter = new StreamWriter(httpWebRequest.GetRequestStream()))
        {
            streamWriter.Write(JsonConvert.SerializeObject(item));
            streamWriter.Flush();
            streamWriter.Close();
        }

        var httpResponse = (HttpWebResponse)httpWebRequest.GetResponse();
        using (var streamReader = new StreamReader(httpResponse.GetResponseStream()))
        {
            var result = streamReader.ReadToEnd();
        }