How do I configure User Assigned Managed Identity for Azure Functions

1. Create a User-Assigned Managed Identity

To create a user-assigned managed identity, you need the Managed Identity Contributor role. Follow these steps:

- Azure Portal:
- Search for Managed Identities.
- Select Add and fill in the details: Subscription, Resource group, Region, and Name.
- Click Review + create and then Create.

- Azure CLI:

bash
  az identity create -g  -n 
  

2. Assign the User-Assigned Identity to the Azure Function

- Azure Portal:
- Navigate to your Azure Function App.
- In the left navigation, select Settings > Identity.
- Under User assigned, click Add.
- Search for the identity you created and select it.
- Click Add. The app will restart.

- Azure CLI or REST API: You need to make a REST PATCH call to Azure API to set the `keyVaultReferenceIdentity` property, as this is not directly available in Azure CLI. Here's an example of how you might do this in Bash using Cloud Shell:

bash
  # Replace placeholders with your actual values
  FUNCTION_APP_NAME="YourFunctionAppName"
  RESOURCE_GROUP="YourResourceGroupName"
  IDENTITY_ID="YourUserAssignedIdentityId"

  # Get the Function App ID
  FUNCTION_APP_ID=$(az functionapp show --name $FUNCTION_APP_NAME --resource-group $RESOURCE_GROUP --query id -o tsv)

  # Update the Function App with the User-Assigned Identity
  az rest --method PATCH --uri $FUNCTION_APP_ID --headers "Content-Type=application/json" --body '{"properties": {"keyVaultReferenceIdentity": {"id": "'$IDENTITY_ID'"}}}'
  

3. Configure Permissions for the Identity

- Assign appropriate Azure roles to the user-assigned managed identity. This can be done through the Azure portal by navigating to the identity, selecting Azure role assignments, and adding roles as needed[5].

4. Use the Managed Identity in Your Azure Function

- Ensure your Azure Function is configured to use the managed identity for authentication. This typically involves using the `DefaultAzureCredential` class in .NET or similar mechanisms in other languages to authenticate with Azure services[6].

5. Verify the Configuration

- Test your Azure Function to ensure it can access resources using the user-assigned managed identity. This might involve checking logs or verifying successful interactions with other Azure services like Key Vault or Azure SQL Database.

Citations:
[1] https://www.red-gate.com/simple-talk/cloud/azure/azure-function-and-user-assigned-managed-identities/
[2] https://learn.microsoft.com/en-us/entra/identity/managed-identities-azure-resources/how-manage-user-assigned-managed-identities
[3] https://learn.microsoft.com/en-us/azure/app-service/overview-managed-identity
[4] https://codebankblog.wordpress.com/2020/06/27/azure-function-with-managed-identity-and-azure-sql-db/
[5] https://inthecloud247.com/configure-a-user-assigned-managed-identity-the-basics/
[6] https://docs.azure.cn/en-us/azure-functions/functions-identity-based-connections-tutorial
[7] https://trendmicro.com/cloudoneconformity/knowledge-base/azure/Functions/azure-function-user-assigned-identity.html
[8] https://github.com/Azure/azure-functions-host/issues/8662