update text for managedidentity afd

Author: duongau

articles/frontdoor/standard-premium/how-to-configure-https-custom-domain.md

@@ -77,13 +77,14 @@ You can also choose to use your own TLS certificate. Your TLS certificate must m
 
 Create a separate Azure Key Vault instance in which you store your Azure Front Door TLS certificates. For more information, see [Create a Key Vault instance](../../key-vault/general/quick-create-portal.md). If you already have a certificate, you can upload it to your new Key Vault instance. Otherwise, you can create a new certificate through Key Vault from one of the certificate authority (CA) partners.
 
-> [!WARNING]
-> Azure Front Door currently only supports Key Vault in the same subscription. Selecting Key Vault under a different subscription results in a failure.
+There are currently two ways to authenticate Azure Front Door to access your Key Vault:
 
-Other points to note about certificates:
+- **Managed identity**: Azure Front Door uses a managed identity to authenticate to your Key Vault. This method is recommended because it's more secure and doesn't require you to manage credentials. For more information, see [Use managed identities in Azure Front Door](../managed-identity.md). Skip to [Select the certificate for Azure Front Door to deploy](#select-the-certificate-for-azure-front-door-to-deploy) if you're using this method.
+- **App registration**: Azure Front Door uses an app registration to authenticate to your Key Vault. This method is being deprecated and will be retired in the future. For more information, see [Use app registration in Azure Front Door](#register-azure-front-door).
 
-* Azure Front Door doesn't support certificates with elliptic curve cryptography algorithms. Also, your certificate must have a complete certificate chain with leaf and intermediate certificates. The root CA also must be part of the [Microsoft Trusted CA List](https://ccadb-public.secure.force.com/microsoft/IncludedCACertificateReportForMSFT).
-* We recommend that you use [managed identity](../managed-identity.md) to allow access to your Key Vault certificates because app registration will be retired in the future.
+> [!WARNING]
+> *Azure Front Door currently only supports Key Vault in the same subscription. Selecting Key Vault under a different subscription results in a failure.
+> * Azure Front Door doesn't support certificates with elliptic curve cryptography algorithms. Also, your certificate must have a complete certificate chain with leaf and intermediate certificates. The root CA also must be part of the [Microsoft Trusted CA List](https://ccadb-public.secure.force.com/microsoft/IncludedCACertificateReportForMSFT).
 
 #### Register Azure Front Door