List Blobs using Azure API Rest returns Forbidden

Question

I'm trying to get the list of blobs inside a folder using the Azure Rest API and I'm getting 403 Forbidden for a problem building the authorization signature for the Shared Key.

Here is my source code:

// Build the authorization signature
var requestDate = DateTime.UtcNow.ToString("R");
var canonicalizedResource = $"/{accountName}/{containerName} \ncomp:list\nprefix:contacts/{contactId}\nrestype:container";
var stringToSign = $"GET\n\n\n\n\n\n\n\n\n\n\n\n{requestDate}\nx-ms-version:2023-08-03\n{canonicalizedResource}";
string signature;
using (var hmac = new HMACSHA256(Convert.FromBase64String(accessKey)))
{
    var dataToHmac = Encoding.UTF8.GetBytes(stringToSign);
    signature = Convert.ToBase64String(hmac.ComputeHash(dataToHmac));
}

// Make the HTTP GET request
var url = $"https://{accountName}.blob.core.windows.net/{containerName}?restype=container&comp=list&prefix=contacts/{contactId}";
using (var client = new HttpClient())
{
    client.DefaultRequestHeaders.Add("x-ms-version", "2023-08-03");
    client.DefaultRequestHeaders.Add("x-ms-date", requestDate);
    client.DefaultRequestHeaders.Add("Authorization", $"SharedKey {accountName}:{signature}");

    var response = await client.GetAsync(url);

    // Process the response
    if (response.IsSuccessStatusCode)
    {
        var responseContent = await response.Content.ReadAsStringAsync();
        Console.WriteLine("List of blobs in the container:");
        Console.WriteLine(responseContent);
    }
    else
    {
        Console.WriteLine($"Error getting list of blobs. Status code: {response.StatusCode}");
    }
}

Am I missing something?

Can you please try with the following: var stringToSign = $"GET\n\n\n\n\n\n\n\n\n\n\n\nx-ms-date:{requestDate}\nx-ms-version:2023-08-03\n{canonicalizedResource}";. I added x-ms-date: to your stringToSign. — Gaurav Mantri
– Gaurav Mantri, Commented Apr 15, 2024 at 11:41

Venkatesan · Accepted Answer · 2024-04-15 12:17:53Z

List Blobs using Azure API Rest returns Forbidden.

I agree with Gaurav Mantri's comment. The above error occurs when you pass the wrong parameters in stringtosign in the code.

Here is the modified code to list the blob in a particular folder from Azure Blob Storage:

Code:

using System.Security.Cryptography;
using System.Text;
using System.Xml.Linq;

class Program
{
    static async Task Main(string[] args)
    {
        var accountName = "venkat123";
        var containerName = "test";
        var contactId = "contacts/ContactId";
        var accessKey = "your access key";
        var apiversion = "2023-08-03";

        
        DateTime dt = DateTime.UtcNow;
        string StringToSign = String.Format("GET\n"
            + "\n" // content encoding
            + "\n" // content language
            + "\n" // content length
            + "\n" // content md5
            + "\n" // content type
            + "\n" // date
            + "\n" // if modified since
            + "\n" // if match
            + "\n" // if none match
            + "\n" // if unmodified since
            + "\n" // range
        + "x-ms-date:" + dt.ToString("R") + "\nx-ms-version:" + apiversion + "\n" // headers
            + "/{0}/{1}\ncomp:list\nprefix:{2}\nrestype:container", accountName, containerName,contactId);
        string signature;
        using (var hmac = new HMACSHA256(Convert.FromBase64String(accessKey)))
        {
            var dataToHmac = Encoding.UTF8.GetBytes(StringToSign);
            signature = Convert.ToBase64String(hmac.ComputeHash(dataToHmac));
        }

        // Make the HTTP GET request
        var url = $"https://{accountName}.blob.core.windows.net/{containerName}?restype=container&comp=list&prefix={contactId}";
        using (var client = new HttpClient())
        {
            client.DefaultRequestHeaders.Add("x-ms-version", "2023-08-03");
            client.DefaultRequestHeaders.Add("x-ms-date", dt.ToString("R"));
            client.DefaultRequestHeaders.Add("Authorization", $"SharedKey {accountName}:{signature}");

            var response = await client.GetAsync(url);

            // Process the response
            if (response.IsSuccessStatusCode)
            {
                var responseContent = await response.Content.ReadAsStringAsync();
                var xmlDoc = XDocument.Parse(responseContent);
                Console.WriteLine("List of blobs in the container:");
                Console.WriteLine(xmlDoc.ToString(SaveOptions.None));
            }
            else
            {
                Console.WriteLine($"Error getting list of blobs. Status code: {response.StatusCode}");
            }
        }
    }
}

Output:

List of blobs in the container:
<EnumerationResults ServiceEndpoint="https://venkat123.blob.core.windows.net/" ContainerName="test">
  <Prefix>ContactId</Prefix>
  <Blobs>
    ...
  </Blobs>
  <NextMarker />
</EnumerationResults>

Blobs in the container

Reference: List Blobs (REST API) - Azure Storage | Microsoft Learn

It seems that the problem was caused by the string interpolation on a single line, in addition to the header x-ms-date not being correctly added. Modifying the way stringToSign is constructed has worked. Thank you

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