Add context about new sign-in screen

As part of Microsoft's general commitment to security hardening, we are adding a new screen to the auto-acceleration and smartlinks sign-in flows. This screen is called the domain confirmation dialog and provides the user with an opportunity to confirm the domain of the tenant in which they are signing in to. Since this is a new screen being added to the auto-acceleration/smartlinks sign-in UI, we need to call this out in our documentation so customers can avoid concern when they see this new screen. 
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cc: @omondiatieno

Author: nickludwig

articles/active-directory/manage-apps/configure-authentication-for-federated-users-portal.md

@@ -28,6 +28,11 @@ Some organizations configure domains in their Azure AD tenant to federate with a
 
 For federated users with cloud-enabled credentials, such as SMS sign-in or FIDO keys, you should prevent sign-in auto-acceleration. See [Disable auto-acceleration sign-in](prevent-domain-hints-with-home-realm-discovery.md) to learn how to prevent domain hints with HRD. 
 
+> [!IMPORTANT]
+> Starting April 2023, organizations who use auto-acceleration or smartlinks may begin to see a new screen added to the sign-in UI. This screen, termed the Domain Confirmation Dialog, is part of Microsoft's general commitment to security hardening and requires the user to confirm the domain of the tenant in which they are signing in to. If you see the Domain Confirmation Dialog and do not recognize the tenant domain listed, you should cancel the authentication flow and contact your IT Admin.
+> 
+> While the Domain Confirmation Dialog does not need to be shown for every instance of auto-acceleration or smartlinks, the presence of the Domain Confirmation Dialog means auto-acceleration and smartlinks can no longer proceed seamlessly when shown. Finally, given Microsoft identity platform manages the auto-acceleration sign-in flow end-to-end, the introduction of the Domain Confirmation Dialog should not result in any application breakages. 
+
 ## Prerequisites
 
 To configure HRD policy for an application in Azure AD, you need: