[iOS/Swift] generate sas token for Http Authorization to Azure IoT Hub

Question

Please share Swift sample code to generate sas token for Http Authorization to Azure IoT Hub.

Answer 1

Hello @Live Kim ,

it seems you want to access the Azure IoT Hub Rest API.

This is just based on HTTP calls where the security is done using a SAS key.

I do not have an iOS/Swift example, an example of this call using CURL is shown here.

A C# example looks like this:

using System;  
using System.Net;  
using System.Net.Http;  
using System.Security.Cryptography;  
using System.Text;  
  
private static void Main(string[] args)  
{  
    var jsonString = TestGetIdentity("[full iothub connection string]", "[device name]");  
  
    Console.WriteLine($"Press a key to exit for {jsonString}");  
  
    Console.ReadKey();  
}  
  
private static string TestGetIdentity(string cs, string deviceId)  
{  
    var sas = ConstructToken(cs);  
  
    var fullIotHubName = cs.Split(';')[0].Substring(9); // "{shortIoTHubName}.azure-devices.net";  
    string shortIoTHubName = fullIotHubName.Split('.')[0];  
    var url = $"https://{shortIoTHubName}.azure-devices.net/devices/{deviceId}?api-version=2020-05-31-preview";  
  
    using var client = new HttpClient();  
    client.DefaultRequestHeaders.Add("Authorization", sas);  
    var req = new HttpRequestMessage(HttpMethod.Get, url);  
  
    using var res = client.SendAsync(req).Result;  
    return res.Content.ReadAsStringAsync().Result;  
              
}  
  
private static string ConstructToken(string connectionStringIoTHub)  
{  
    var fullIotHubName = connectionStringIoTHub.Split(';')[0].Split('=')[1];  
    var policyName = connectionStringIoTHub.Split(';')[1].Split('=')[1];  
    var key = connectionStringIoTHub.Split(';')[2].Replace("SharedAccessKey=", string.Empty);  
  
    int expiryInSeconds = 3600;  
  
    var fromEpochStart = DateTime.UtcNow - new DateTime(1970, 1, 1);  
    var expiry = Convert.ToString((int)fromEpochStart.TotalSeconds + expiryInSeconds);  
  
    var stringToSign = $"{WebUtility.UrlEncode(fullIotHubName)}\n{expiry}";  
  
    var hmac = new HMACSHA256(Convert.FromBase64String(key));  
    var signature = Convert.ToBase64String(hmac.ComputeHash(Encoding.UTF8.GetBytes(stringToSign)));  
  
    var token = $"SharedAccessSignature sr={WebUtility.UrlEncode(fullIotHubName)}&sig={WebUtility.UrlEncode(signature)}&se={expiry}&skn={policyName}";  
  
    return token;  
}