IoTHub Device Http Client in one file

IoTHubHttpClient.cs

namespace DeviceHttpDemo;

public class Config
{
    public string host = "";
    public string did = "";
    public string key = "";
}

internal class SasAuth
{
    const string apiversion_2020_09_30 = "2020-09-30";
    internal static string GetUserName(string hostName, string deviceId) =>
        $"{hostName}/{deviceId}/?api-version={apiversion_2020_09_30}";
    internal static string CreateSasToken(string resource, string sasKey, int minutes)
    {
        static string Sign(string requestString, string key)
        {
            using var algorithm = new System.Security.Cryptography.HMACSHA256(Convert.FromBase64String(key));
            return Convert.ToBase64String(algorithm.ComputeHash(System.Text.Encoding.UTF8.GetBytes(requestString)));
        }
        var expiry = DateTimeOffset.UtcNow.AddMinutes(minutes).ToUnixTimeSeconds().ToString();
        var sig = System.Net.WebUtility.UrlEncode(Sign($"{resource}\n{expiry}", sasKey));
        return $"SharedAccessSignature sr={resource}&sig={sig}&se={expiry}";
    }

    internal static (string username, string password) GenerateHubSasCredentials(string hostName, string deviceId, string sasKey,int minutes = 60) =>
        (GetUserName(hostName, deviceId), CreateSasToken($"{hostName}/devices/{deviceId}", sasKey, minutes));
}

internal class IoTHubHttpClient
{
    readonly Config _config;
    public IoTHubHttpClient(Config c) => _config = c;
    static string? ToJson(object o) => (o is string) ? o as string : System.Text.Json.JsonSerializer.Serialize(o);

    public async Task<HttpResponseMessage> SendTelemetryAsync(object payload, string compo = "")
    {
        (_, string token) = SasAuth.GenerateHubSasCredentials(_config.host, _config.did, _config.key);
        string urlTelemetry = $"https://{_config.host}/devices/{_config.did}/messages/events?api-version=2020-09-30";

        var req = new HttpRequestMessage(HttpMethod.Post, urlTelemetry)
        {
            Headers = { { "authorization", token } }
        };

        if (!string.IsNullOrEmpty(compo))
        {
            req.Headers.Add("dt-subject", compo);
        }

        var serializedPayload = ToJson(payload);
        if (serializedPayload != null)
        {
            req.Content = new StringContent(serializedPayload, System.Text.Encoding.UTF8, "application/json");
        }

        return await new HttpClient().SendAsync(req);
    }
}