Update managed identity credential

Author: baanders

articles/digital-twins/how-to-authenticate-client.md

@@ -5,7 +5,7 @@ titleSuffix: Azure Digital Twins
 description: Learn how to write authentication code in a client application
 author: baanders
 ms.author: baanders # Microsoft employees only
-ms.date: 02/22/2022
+ms.date: 03/01/2023
 ms.topic: how-to
 ms.service: digital-twins
 
@@ -41,7 +41,7 @@ To continue, you'll need a client app project in which you write your code. If y
 Three common credential-obtaining methods in `Azure.Identity` are:
 
 * [DefaultAzureCredential](/dotnet/api/azure.identity.defaultazurecredential?view=azure-dotnet&preserve-view=true) provides a default `TokenCredential` authentication flow for applications that will be deployed to Azure, and is **the recommended choice for local development**. It also can be enabled to try the other two methods recommended in this article; it wraps `ManagedIdentityCredential` and can access `InteractiveBrowserCredential` with a configuration variable.
-* [ManagedIdentityCredential](/dotnet/api/azure.identity.managedidentitycredential?view=azure-dotnet&preserve-view=true) works great in cases where you need [managed identities (MSI)](../active-directory/managed-identities-azure-resources/overview.md), and is a good candidate for working with Azure Functions and deploying to Azure services.
+* [ManagedIdentityCredential](/dotnet/api/azure.identity.managedidentitycredential?view=azure-dotnet&preserve-view=true) works well in cases where you need [managed identities (MSI)](../active-directory/managed-identities-azure-resources/overview.md), and is a good candidate for working with Azure Functions and deploying to Azure services.
 * [InteractiveBrowserCredential](/dotnet/api/azure.identity.interactivebrowsercredential?view=azure-dotnet&preserve-view=true) is intended for interactive applications, and can be used to create an authenticated SDK client.
 
 The rest of this article shows how to use these methods with the [.NET (C#) SDK](/dotnet/api/overview/azure/digitaltwins.core-readme).
@@ -76,16 +76,18 @@ Here's a code sample to add a `DefaultAzureCredential` to your project:
 
 ### ManagedIdentityCredential method
 
-The [ManagedIdentityCredential](/dotnet/api/azure.identity.managedidentitycredential?view=azure-dotnet&preserve-view=true) method works great in cases where you need [managed identities (MSI)](../active-directory/managed-identities-azure-resources/overview.md)—for example, when [authenticating with Azure Functions](#authenticate-azure-functions).
+The [ManagedIdentityCredential](/dotnet/api/azure.identity.managedidentitycredential?view=azure-dotnet&preserve-view=true) method works well in cases where you need [managed identities (MSI)](../active-directory/managed-identities-azure-resources/overview.md)—for example, when [authenticating with Azure Functions](#authenticate-azure-functions).
 
-This means that you may use `ManagedIdentityCredential` in the same project as `DefaultAzureCredential` or `InteractiveBrowserCredential`, to authenticate a different part of the project.
+This means that you can use `ManagedIdentityCredential` in the same project as `DefaultAzureCredential` or `InteractiveBrowserCredential`, to authenticate a different part of the project.
 
 To use the default Azure credentials, you'll need the Azure Digital Twins instance's URL ([instructions to find](how-to-set-up-instance-portal.md#verify-success-and-collect-important-values)). You may also need an [app registration](./how-to-create-app-registration.md) and the registration's [Application (client) ID](./how-to-create-app-registration.md#collect-client-id-and-tenant-id).
 
 In an Azure function, you can use the managed identity credentials like this:
 
 :::code language="csharp" source="~/digital-twins-docs-samples/sdks/csharp/authentication.cs" id="ManagedIdentityCredential":::
 
+If you're using a user-assigned identity for the function app, enter the client ID of the user-assigned identity as a parameter when creating the credential. If you're using the function app's system-assigned identity to authenticate, you can leave the parameter empty.
+
 ### InteractiveBrowserCredential method
 
 The [InteractiveBrowserCredential](/dotnet/api/azure.identity.interactivebrowsercredential?view=azure-dotnet&preserve-view=true) method is intended for interactive applications and will bring up a web browser for authentication. You can use this method instead of `DefaultAzureCredential` in cases where you require interactive authentication.
@@ -120,9 +122,13 @@ When writing the Azure function, consider adding these variables and code to you
 
     :::code language="csharp" source="~/digital-twins-docs-samples/sdks/csharp/adtIngestFunctionSample.cs" id="HTTP_client":::
 
-* **Managed identity credentials.** Create a managed identity credential that your function will use to access Azure Digital Twins.
+* **Managed identity credentials.** Create a managed identity credential that your function will use to access Azure Digital Twins. 
+
+    If you're using a user-assigned identity for the function app, enter the client ID of the user-assigned identity as a parameter when creating the credential, as shown below:
     :::code language="csharp" source="~/digital-twins-docs-samples/sdks/csharp/adtIngestFunctionSample.cs" id="ManagedIdentityCredential":::
 
+    If you're using the function app's system-assigned identity to authenticate, you can leave the parameter empty.
+
     Later, after publishing the function, you'll make sure the function's identity has permission to access the Azure Digital Twins APIs. For instructions on how to do so, skip ahead to [Assign an access role](#assign-an-access-role).    
 
 * **A local variable _DigitalTwinsClient_.** Add the variable inside your function to hold your Azure Digital Twins client instance. _Don't_ make this variable static inside your class.