HttpClientHelpers.cs

public static class HttpClientHelpers
{
    public static async Task<RestResponse<TResult>> PostJsonAsync<TResult>(this HttpClient client,
        string resource,
        object requestBody)
    {
        var json = requestBody != null ? JsonConvert.SerializeObject(requestBody) : string.Empty;
        var request = new StringContent(json, Encoding.UTF8, "application/json");
        var response = await client.PostAsync(resource, request);
        return await RestResponse<TResult>.FromHttpResponseMessageAsync(response);
    }
}

    public class RestResponse<T>
    {
        public static async Task<RestResponse<T>> FromHttpResponseMessageAsync(HttpResponseMessage response)
            => new RestResponse<T>(await response.Content.ReadAsStringAsync(), response.StatusCode);

        private RestResponse(string responseBody, HttpStatusCode statusCode)
        {
            ResponseBody = responseBody;
            if(responseBody != null)
                Result = JsonConvert.DeserializeObject<T>(responseBody);
            StatusCode = statusCode;
            IsSuccessStatusCode = statusCode.IsSuccessful();
        }

        public string ResponseBody { get; }
        public HttpStatusCode StatusCode { get; }
        public T Result { get; }
        public bool IsSuccessStatusCode { get; }
    }