My colleague Mike Parker has a great new series of posts up on securing Exchange Server 2016 with Azure AD. This option may seem counter-intuitive at a glance, but given that most organisations are on a trajectory from Exchange Server to Exchange Online, this configuration can consolidate access control for e-mail in a single location (for instance, over the duration of a migration or for long-term co-existence). It also means that Azure AD Conditional Access policies can be used for Exchange resources on and off-premises, which improves security while enabling mobility.
This configuration has two parts:
- Get most Exchange Server components to use OAuth 2.0. This is known as Hybrid Modern Authentication.
- Publish Outlook Web App (OWA) and the Exchange Control Panel (ECP) using the Azure AD Application Proxy.
The second step is necessary because these components are not currently supported for Hybrid Modern Authentication. The major pre-requisite for publishing an application with the Azure AD Application Proxy is that it should be authenticated with Kerberos and the Application Proxy Connector machine accounts need to be configured to use Constrained Delegation (KCD) for the OWA and ECP Service Principal Name (SPN). Mike’s article takes you through all of this step-by-step. My post deviates a bit from Mike’s guide to consider the idiosyncrasies of the Exchange Alternative Service Account Credential (ASA), which has underpinned Kerberos in Exchange Server since 2010 SP1. If you are familiar with configuring Kerberos, the ASA will almost certainly hold some surprises. Maybe even a fourth head.