I'm pretty certain that I can do it. What I'm not certain about is whether it can be done. Here are the challenges:

1. User Information Sharing
2. User Session Sharing

The problem is that with both of those challenges, the easy solution lies within the encrypted PHP files (i.e. having the signup php copy the information into the other program on account creation and having login.php create both sessions when a user logs in). I'd have to really look into this to see how much can be done for this (without violating any of vShare's terms).