add asp.net pages to an asp classic website

I have an asp classic web site, i want to add some new code. I would want to begin to code with .net. Is there an easy way of doing this.

I was thinking an iframe that call my .net pages, but how will I share my user that need to be logued in my asp classic web site.

If I would use an iframe, what would be the best technique to share my user. I was thinking of passing the crypted info in query : test.com?users=[mycrypteduser]. But how would I encrypt it ?

Thanks