And here it is:

http://msdn.microsoft.com/en-US/library/windowsphone/develop/jj207032(v=vs.105).aspx

There are samples galore but one you could use to build and make money off of for the phone:

http://code.msdn.microsoft.com/wpapps/Wallet-membership-and-f5ffee3a

Now get busy build apps.

Wallet