HttpClient Sample on posting data.

HttpClientSample.cs

using Newtonsoft.Json;
using System.Collections.Generic;
using System.Net.Http;
using System.Threading.Tasks;

public class Program
{
    public static void Main()
    {
       var task = Login();
       task.Wait();
    }

    private static async Task Login()
    {
        var client = new HttpClient();
        var content = new FormUrlEncodedContent(new[]
        {
            new KeyValuePair<string, string>("grant_type", "password"),
            new KeyValuePair<string, string>("username", "[email protected]"),
            new KeyValuePair<string, string>("password", "password1")
            });
        var result = await client.PostAsync("https://localhost:44305/token", content).ConfigureAwait(false);
        string resultContent = await result.Content.ReadAsStringAsync();
        var tokenResponse = JsonConvert.DeserializeObject<TokenResponse>(resultContent);
    }

}

public class TokenResponse
{
    public string access_token { get; set; }
    public string token_type { get; set; }
    public int expires_in { get; set; }
    public string userName { get; set; }
    public string issued { get; set; }
    public string expires { get; set; }
}