Network Policy and Access Services (NPAS)[1] is a component of Windows Server 2008.
It replaces the Internet Authentication Service (IAS) from Windows Server 2003.
The NPAS server role includes Network Policy Server (NPS), Health Registration Authority (HRA), and Host Credential Authorization Protocol (HCAP).
NPS is a role service in Windows Server 2008 which can function as: NPSEE enables the use of a heterogeneous set of wireless, switch, remote access, or VPN equipment.
[2] When a server running NPS is a member of an Active Directory Domain Services (AD DS) domain, NPS uses the directory service as its user account database and is part of a single sign-on solution.