How to get the url of an uploaded blob using user-assigned managed identities?

Question

I am running a function app that it gets triggered when an item of specific type is uploaded to a storage account, and it processes the item uploaded to it.

A function I wrote needs the url to the blob as an input.

• Before I was passing the url as shown below, and it worked.

https://<storage-account-name>.blob.core.windows.net/<path-to-file-location>/<name-of-uploaded-file>?<sas-token>

• Now, I want to use user-assigned managed identities to access the blob. I can successfully create the credential and service to the blob.
  • The user-assigned managed identity and the Function App have been given Storage Blob Data Contributor permissions on the storage account used.
  • What would the url I need to pass to my function should look like? If I pass only the below, it does not work.

https://<account-name>.blob.core.windows.net/<path_to_file_location>/<name_of_uploaded_file>

My question:

How should I pass the url to the uploaded item to the function, if I am using user-assigned managed identities / shouldn't need a sas token anymore?

Answer 1

Hello @carom-9728

You can use Managed Identity to link Azure Function with Azure Blob storage. You need to enabled Managed Identity in Azure Functions and give it permissions in Azure Storage Account(select the role “Storage Blob Data Contributor” for example).
http://www.klaushaller.net/?p=1312

After that you will be able to download file in code(.Net example):

    var myBlobUrl = " https://<account-name>.blob.core.windows.net/<path_to_file_location>/<name_of_uploaded_file>";  
    BlobClient bc = new BlobClient(new Uri(myBlobUrl), myCredentials);  

    log.LogInformation("**2**");  

    BlobDownloadResult downloadResult = await bc.DownloadContentAsync();  
    string downloadedData = downloadResult.Content.ToString();  

https://learn.microsoft.com/en-us/azure/active-directory/managed-identities-azure-resources/tutorial-linux-vm-access-storage