Exchange 2013 WAp and cross-froest authentication

Hello guys,

I planned to migrate my exchange 2003 users to exchange 2013.

To do this i setup a new forest with a new domain, my question is:

How publish OWA by wap and adfs with cross-forest, because the exchange forest is only a resource forest, do i need Windows 2012 R2 as domain controller on each forest like as read on some forums ?

thanks for your reply.

Jérôme.