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

Posted on by

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);

Leave a comment

This site uses Akismet to reduce spam. Learn how your comment data is processed.