Cisco, AAA, Radius, Active Directory, Windows Server 2012 R2, NAP role, NPS its all going on!
Just a quick note to reference the following video on YouTube. This video demonstrates setting up Active Directory Authentication for Cisco Devices, such as Routers and Switches etc. This is using AAA on the router and RADIUS through the Network Access Policy (NAP) role in Windows Server 2012 R2, this in turn enables a Network Policy Server (NPS). The Windows server (the Radius Server) is registered in Active Directory which allows it to query the domain it is connected too for authenticating users in Active Directory to the Cisco IOS devices. You can control who has access to various network devices through rules created on the NPS. This can in turn be achieved in Active Directory via groups, binding those groups to privilege levels to pass through to deifferent devices.
For example you could have a group in AD called Network Admins which is tied to a prilivelge level 15 group rule in the NPS configuration. This rule would pass through the privilege level 15 setting through to the IOS configuration. Members of this AD group upon succesful authentication would then be granted privilege level 15 access on the router or switch.