string grant_type = "password";

public async Task<Response> Login() {
    var postData = new List<KeyValuePair<string, string>>();
    postData.Add(new KeyValuePair<string, string>("grant_type",
    grant_type));
    postData.Add(new KeyValuePair<string, string>("userName",
    "**********"));
    postData.Add(new KeyValuePair<string, string>("password",
    "**********"));
    var content = new FormUrlEncodedContent(postData);
    var weburl = "https://**.**.***.***:*****/*****/login";
    var response = await PostResponse<Response>(weburl, content);
    return response;
}

public async Task<Response> PostResponse<Response>(string weburl,
FormUrlEncodedContent content) {
    var response = await client.PostAsync(weburl, content);
    var jsonResult = response.Content.ReadAsStringAsync().Result;
    Response responseObject = JsonConvert.DeserializeObject<Response>
    (jsonResult);
    return responseObject;
}