Recently, MS have spoken in build 2013 conference session titled "Securing Windows Store Applications and REST Services with Active Directory" and video posted at http://channel9.msdn.com/Events/Build/2013/3-518
This session talks about new OAuth end point as part of ADFS Windows Server 2012 server. And token validation in ASP.NET Web API using AAL and for this Windows Azure Active Directory is required.
But I would like to try on premise ADFS of Server 2012.
Which lib should I use with in MS framework to validate the token in ASP.NET Web API 2?
What is the token format you plan to use? Will it be the SAML as-is or you plan to transform it to may be JWT? Azure ACS can give you JWT or you can use thinktecture identity server. Check this out. SAML can get bulky at times and you can have problem transporting them in an HTTP header depending on the token size.
If you plan to use SAML, you can use WIF classes SecurityTokenHandlerCollection, etc. For JWT, there is a library available with a long name of "JSON Web Token Handler For the Microsoft .Net Framework 4.5". Check this out as well.