RhSolutions-AddIn/src/Services/RhDatabaseClient.cs

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

namespace RhSolutions.Services
{
    public static class RhDatabaseClient
    {
        private static HttpClient httpClient = RhSolutionsAddIn.httpClient;

        public static async Task<object> GetProduct(string line)
        {
            string request = @"https://rh.cebotari.ru/api/search?query=" + line;

            ServicePointManager.SecurityProtocol =
                SecurityProtocolType.Tls12 |
                SecurityProtocolType.Tls11 |
                SecurityProtocolType.Tls;

            string response = await httpClient.GetStringAsync(request);

            var products = JsonConvert.DeserializeObject<IEnumerable<DbProduct>>(response);

            var product = products.FirstOrDefault();

            if (product == null)
            {
                return null;
            }
            else
            {
                return $"{product.productSku} {product.name}";
            }
        }

        private class DbProduct
        {
            public string productSku { get; set; }
            public string name { get; set; }
        }
    }
}