Update app-service-run-from-package-via-identity.md

Author: v-dirichards

includes/app-service-run-from-package-via-identity.md

@@ -16,3 +16,5 @@ To enable the package to be fetched using the identity:
 1. Grant the identity the [Storage Blob Data Reader](/azure/role-based-access-control/built-in-roles#storage-blob-data-reader) role with scope over the package blob. See [Assign an Azure role for access to blob data](/azure/storage/blobs/assign-azure-role-data-access) for details on creating the role assignment.
 
 1. Set the `WEBSITE_RUN_FROM_PACKAGE` application setting to the blob URL of the package. This URL is usually of the form `https://{storage-account-name}.blob.core.windows.net/{container-name}/{path-to-package}` or similar.
+
+1. If you wish to specify a user-assigned identity, you can set the `WEBSITE_RUN_FROM_PACKAGE_BLOB_MI_RESOURCE_ID` app setting to the resource ID of that identity. The setting can also accept "SystemAssigned" as a value, although this is the same as omitting the setting altogether. A resource ID is a standard representation for a resource in Azure. For a user-assigned managed identity, that is going to be `/subscriptions/subid/resourcegroups/rg-name/providers/Microsoft.ManagedIdentity/userAssignedIdentities/identity-name`. The resource ID of a user-assigned managed identity can be obtained in the **Settings** -> **Properties** -> **ID for the user assigned managed identity**.