/azure-prepare

Storage - Access Patterns

Prerequisites for Granting Storage Access

⚠️ Important: To assign storage roles to managed identities, you need:

• User Access Administrator or Owner role on the Storage Account (or parent resource group/subscription)
• The role must include the Microsoft.Authorization/roleAssignments/write permission

Common scenarios:

• Granting Storage Blob Data Owner to a Web App or Function App's managed identity (System Assigned or User Assigned)
• Adding read/write access to blobs, queues, and tables for application workloads
• Allowing user identities (developers, data admins) access in dev/test environments
• Allowing applications to access storage using managed identity instead of connection strings

Scope best practices:

• Grant roles at the smallest scope possible (e.g., specific storage account, not resource group or subscription)
• Avoid broad scopes (Resource Group, Subscription, Tenant) unless absolutely necessary
• Prefer resource-level assignments for production workloads

Managed identity types:

• System Assigned: Automatically created with the resource (Web App, Function). Default when using DefaultAzureCredential.
• User Assigned: Standalone identity that can be shared across resources. Requires additional configuration:
  • Set AZURE_CLIENT_ID app setting to the User Assigned Managed Identity's client ID
  • Configure identity in Bicep with both type: 'SystemAssigned, UserAssigned' and userAssignedIdentities

If you encounter AuthorizationFailed errors when assigning roles, ensure you have User Access Administrator or Owner permissions at the target scope.

Managed Identity Role Assignment

resource storageRoleAssignment 'Microsoft.Authorization/roleAssignments@2022-04-01' = {
  name: guid(storageAccount.id, principalId, 'Storage Blob Data Contributor')
  scope: storageAccount
  properties: {
    roleDefinitionId: subscriptionResourceId('Microsoft.Authorization/roleDefinitions', 'ba92f5b4-2d11-453d-a403-e96b0029c9fe')
    principalId: principalId
    principalType: 'ServicePrincipal'
  }
}

Storage Roles

SDK Connection Patterns

Node.js

const { BlobServiceClient } = require("@azure/storage-blob");

const blobServiceClient = BlobServiceClient.fromConnectionString(
  process.env.AZURE_STORAGE_CONNECTION_STRING
);
const containerClient = blobServiceClient.getContainerClient("uploads");

Python

from azure.storage.blob import BlobServiceClient

blob_service_client = BlobServiceClient.from_connection_string(
    os.environ["AZURE_STORAGE_CONNECTION_STRING"]
)
container_client = blob_service_client.get_container_client("uploads")

.NET

var blobServiceClient = new BlobServiceClient(
    Environment.GetEnvironmentVariable("AZURE_STORAGE_CONNECTION_STRING")
);
var containerClient = blobServiceClient.GetBlobContainerClient("uploads");

Managed Identity Access

Use DefaultAzureCredential for local development (in production, use ManagedIdentityCredential — see auth-best-practices.md):

const { DefaultAzureCredential } = require("@azure/identity");
const { BlobServiceClient } = require("@azure/storage-blob");

const client = new BlobServiceClient(
  `https://${accountName}.blob.core.windows.net`,
  new DefaultAzureCredential()
);