CloudKit Server-to-server API in C#

CloudKit.cs

using System;
using System.Net.Http;
using System.Security.Cryptography;
using System.Text;
using System.Threading.Tasks;
using Newtonsoft.Json;
using Newtonsoft.Json.Linq;

namespace YoApp
{
    public class CloudKit
    {
        string keyId;
        string stage;
        string container;
        IHttpClientFactory httpClientFactory;
        ECDsa key;
        public CloudKit(string apiStage, IHttpClientFactory httpClientFactory)
        {
            this.httpClientFactory = httpClientFactory;
            container = "iCloud.app.name";
            if (apiStage == "Prod")
            {
                keyId = "a5cf........";
                stage = "production";
            } else
            {
                keyId = "b336.........";
                stage = "development";
            }
            key = ECDsa.Create();
            key.ImportECPrivateKey(Convert.FromBase64String(Environment.GetEnvironmentVariable("SECRET_KEY_BASE64")), out _);
        }

        public async Task<JObject> makeRequest(string endpoint, dynamic arguments)
        {
            var httpClient = httpClientFactory.CreateClient();
            httpClient.BaseAddress = new Uri("https://api.apple-cloudkit.com");
            var path = $"/database/1/{container}/{stage}/public/{endpoint}";

            var datetime = DateTime.UtcNow;
            var formattedDate = datetime.ToString("yyyy-MM-ddTHH:mm:ssZ");

            var body = Encoding.UTF8.GetBytes(JsonConvert.SerializeObject(arguments));
            var bodyHash = Convert.ToBase64String(SHA256.HashData(body));
            var signatureInput = $"{formattedDate}:{bodyHash}:{path}";
            var signature = Convert.ToBase64String(key.SignData(Encoding.UTF8.GetBytes(signatureInput), HashAlgorithmName.SHA256, DSASignatureFormat.Rfc3279DerSequence));

            using (var request = new HttpRequestMessage(HttpMethod.Post, path))
            {
                request.Content = new ByteArrayContent(body);
                request.Headers.Add("X-Apple-CloudKit-Request-KeyID", keyId);
                request.Headers.Add("X-Apple-CloudKit-Request-ISO8601Date", formattedDate);
                request.Headers.Add("X-Apple-CloudKit-Request-SignatureV1", signature);

                var response = await httpClient.SendAsync(request);

                var data = await response.Content.ReadAsStringAsync();
                return JObject.Parse(data);
            }

        }
    }
}