You are developing a Windows Store app that uses the Windows Push Notification Service (WNS) to
send toast notifications.
You need to ensure that the requests that the app sends to the WNS follow the authorization
standard that WNS supports.
Which authorization standard should you use?

A.
ADFS

B.
ws-Trust

C.
openID

D.
OAuth 2.0

Explanation:
http://msdn.microsoft.com/en-us/library/windows/apps/hh913756.aspx