Session Fixation Am i secure?

Question

I am trying to implement security for my project that prevents session fixation.

As i have no access to the component (a filter from a certain library, lets call it MagicFilter) that handles the whole session-creation and validation, i was trying to find out another way of possibly doing it.

Now, consider this scenario for my session:

• User requests the login-page
• MagicFilter sets a cookie with a JSESSIONID etc
• other filters do some work ...
• Java Spring MVC, so as last step before the user sees the LoginView i have access to stuff in my LoginController. Here i .invalidate() the session right before i return the view.

So basically the user never has a real and valid session-ID while at the login-page. Only after he logs in the MagicFilter assigns another session-ID which will then be sticked to, as i only invalide() the session-ID in my LoginController.

But this feels very rough and i kind of had to "hack" around the automatic process of the MagicFilter. Can anyone see if this should be safe in terms of session fixation or not?