Android In-app billing to unlock digital content, but how

I'm trying to get androids new In-APP Billing to work with unlockable content. For example, the user can unlock special content for a limited time. The content comes from a web service, the problem I have is, how do I know when the user can view the content?

Because the user can buy it multiple times I use the items unmanaged. So I somehow have to store the users information in my s开发者_运维问答ervice, so I can provide content when he is allowed to.

The problem is that I don't have any information about the user, no ID, only a orderid which is not remembered by google. So if he changes phone or wipes the database the access is lost.

What is the best possible way ensure the user has access to the content?

The only way i can think of is to store it on a remote server, where you could keep the data of who has what.

To create an ID for a user you could do some type of UUID creation see:

http://android-developers.blogspot.com/2011/03/identifying-app-installations.html