To improve performances, I'd like to add a fairly long Cache-Control (up to 30 minutes) to each page since they do not change often. However, each page also displays the name of the user logged in (like this website).

The problem is when the user logs in or logs out: the user name must change. How can I change the user name after each login/logout action while keeping a long Cache-Control?

Here are the solutions I can think of:

• Ajax request (not cached) to retrieve and display the user name. If I have 2 requests (/user?registered and /user?new), they could be cached as well. But I am afraid this extra request would nullify my caching performance-wise
• Add a unique URL variable (?time=) to make the URL different, and cancel the cache. However, I would have to add this variable to all links on my webpage, not very convenient code-wise

This problems becomes greater if I actually have more content that is not the same for registered users and new users.