How to maintain a session between parent and iFrame?

Hello.  I've come accross a major problem.  I have a user which is already authenticated.  I want to store some data in his Session for which I can use within a page embedded in an iFrame.  The problem is that when I embed and load the iFrame, the users Session Data is different.  Well, the user has a new session.
 
Can someone tell me how to keep a users Session the same between the Parent Page and the IFrame?  Both pages are on the same sever and apart of the same app.
 
Thanks,
stringa 
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