Tag Archives: SHA256

.NET nanoFramework RAK11200 – Azure IoT Hub HTTP SAS Tokens – Revisited

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Several times my client apps inspired by Azure IoT Hub HTTP Basic have not worked because I have failed to correctly trim the Azure IoT Hub Shared Access Signature(SAS) generated with tools like Azure Command Line az iot hub generate-sas-token, Azure IoT Tools for Visual Studio Code or Azure IoT Explorer.

The tokens are quite long but “the only “important” parts are the resource(sr), signature(sig) and expiry(se) values. If the connection string is generated 

HostName=01234567890123456789.azure-devices.net;DeviceId=RAK11200-RAK19001;SharedAccessSignature=SharedAccessSignature sr=01234567890123456789.azure-devices.net%2Fdevices%2FRAK11200-RAK19001&sig=ABCDEFGHIJLMNOPQRSTUVWXYZ1234567890abcdefghijklmnopqrs&se=1663810576

The final version of the application constructs the Azure IoT Hub Shared Access Signature(SAS) with the AzureIoTHubHostName, DeviceID, signature(sig) & expiry(se) values in the config.cs file.

public class Config
{
   public const string DeviceID = "RAK11200-RAK19001";
   public const string SasSignature = "..."; // sig
   public const string SasExpiryTime = "..."; // se

   public const string AzureIoTHubHostName = "..";
   public const string Ssid = "...";
   public const string Password = "..";
   ...
}

 _httpClient = new HttpClient
{
   SslProtocols = System.Net.Security.SslProtocols.Tls12,
   HttpsAuthentCert = new X509Certificate(Config.DigiCertBaltimoreCyberTrustRoot),
   BaseAddress = new Uri($"https://{Config.AzureIoTHubHostName}.azure-devices.net/devices/{Config.DeviceID}/messages/events?api-version=2020-03-13"),
};

string sasKey = $"SharedAccessSignature sr={Config.AzureIoTHubHostName}.azure-devices.net%2Fdevices%2F{Config.DeviceID}&sig={Config.SasSignature}&se={Config.SasExpiryTime}";

_httpClient.DefaultRequestHeaders.Add("Authorization", sasKey);

.NET nanoFramework RAK11200 – Azure IoT Hub HTTP SAS Tokens

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This is the simplest .NET nanoFramework Azure IoT Hub client I could come up with (inspired by this nanoFramework sample).

My test setup was a RAKwireless RAK11200 WisBlock WiFi Module, RAK5005 WisBlock Base Board or RAK19001 WisBlock Dual IO Base Board and RAK1901 WisBlock Temperature and Humidity Sensor

RAK112000+RAK5005-O+RAK1901 Test rig
RAK112000+RAK19001+RAK1901 Test rig

I used a RAK1901 WisBlock Temperature and Humidity Sensor because it has nanoFramework.IoTDevice library support

public class Program
{
    private static TimeSpan SensorUpdatePeriod = new TimeSpan(0, 30, 0);

    private static HttpClient _httpClient;

    public static void Main()
    {
        Debug.WriteLine("devMobile.IoT.RAK.Wisblock.AzureIoHub.RAK1901 starting");

        Configuration.SetPinFunction(Gpio.IO04, DeviceFunction.I2C1_DATA);
        Configuration.SetPinFunction(Gpio.IO05, DeviceFunction.I2C1_CLOCK);

        if (!WifiNetworkHelper.ConnectDhcp(Config.Ssid, Config.Password, requiresDateTime: true))
        {
            if (NetworkHelper.HelperException != null)
            {
                Debug.WriteLine($"WifiNetworkHelper.ConnectDhcp failed {NetworkHelper.HelperException}");
            }

            Thread.Sleep(Timeout.Infinite);
        }

        _httpClient = new HttpClient
        {
            SslProtocols = System.Net.Security.SslProtocols.Tls12,
            HttpsAuthentCert = new X509Certificate(Config.DigiCertBaltimoreCyberTrustRoot),
            BaseAddress = new Uri($"https://{Config.AzureIoTHubHostName}.azure-devices.net/devices/{Config.DeviceID}/messages/events?api-version=2020-03-13"),
        };
        _httpClient.DefaultRequestHeaders.Add("Authorization", Config.SasKey);

        I2cConnectionSettings settings = new(1, Shtc3.DefaultI2cAddress);
        I2cDevice device = I2cDevice.Create(settings);
        Shtc3 shtc3 = new(device);

        while (true)
        {
            if (shtc3.TryGetTemperatureAndHumidity(out var temperature, out var relativeHumidity))
            {
                Debug.WriteLine($"Temperature {temperature.DegreesCelsius:F1}°C  Humidity {relativeHumidity.Value:F0}%");

                string payload = $"{{\"RelativeHumidity\":{relativeHumidity.Value:F0},\"Temperature\":{temperature.DegreesCelsius.ToString("F1")}}}";

                try
                {
                    using (HttpContent content = new StringContent(payload))
                    using (HttpResponseMessage response = _httpClient.Post("", content))
                    {
                        Console.WriteLine($"{DateTime.UtcNow:HH:mm:ss} Response code:{response.StatusCode}");

                        response.EnsureSuccessStatusCode();
                    }
                }
                catch(Exception ex)
                {
                    Debug.WriteLine($"Azure IoT Hub POST failed:{ex.Message}");
                }
            }

            Thread.Sleep(SensorUpdatePeriod);
        }
    }
}

I generated the Azure IoT Hub Shared Access Signature(SAS) Tokens (10800 minutes is 1 week) with Azure IoT Explorer (Trim the SAS key so it starts with SharedAccessSignature sr=….)

Azure IoT Explorer SAS Token Generation

I was using Azure IoT Explorer to monitor the telemetry and found that the initial versions of the application would fail after 6 or 7 hours. After reviewing the code I added a couple of “using” statements which appear to have fixed the problem as the soak test has been running for 12hrs, 24hrs, 36hrs, 48hrs, 96hrs…