We're developing a website and we've encountered this issue: for this website there are 2 types of users: the customer and an administrator. The administrator can see all products (e.g. including expired products) while the customer can only see a subset. 

We're achieving this through user restrictions for the customer group and the administrator group. Products are displayed according to the user logged in. If he belongs to the customer group then a set of restrictions apply, if he belongs to the administrator group another set of restrictions applies. 

Now, it can be the case that an administrator wants to see the website from a customer perspective. Since it's impossible to have two users in the same session, currently the administrator is logged out by the system and is logged in as a user in the customer group. This situation however is not ideal.

Has anyone ever encountered this situation before and is there a clean solution somehow? The underlying technology is a custom server based on Tomcat 6.0.29. We're developing using Java. 

Thanks :)
Krt\_Malta