APM recreating session when user hits default URL

We're trying to build out our APM configuration using AD authentication, and I've found that if I go to the main page (e.g. https://portal.example.com), I'll get the logon page as expected, and once logged in will get my webtop. However, if I again try to access that same URL (e.g. https://portal.example.com) (use case is that a user would log in and then browse the internet and then want to come back to their webtop) they are presented again with the login screen instead of being redirected to their webtop (since they would already have an active session).

Is there a way to make this work so that if an authenticated session already exists, they will be redirected to the webtop? (I've tried adding a check before the logon page, but the session gets recreated before the policy even begins.

Thanks in advance!