APM - apply macro rule based on a specific link selection

I'm not even sure where to start with this question. I have an Access Policy using the F5 as a saml sp. It's relatively simple. The user hits the F5 gets the saml auth (which sends the request to an external IDP). Gets the response back and am doing a variable assign so that I can pass the username on the serverside for kerberos authentication. ALL OF THIS WORKS FINE. However i have an application that is linked to and served up via an iframe within sharepoint that doesn't support kerberos. Soooo, I need to make it so that when users who have already authenticated and are in sharepoint click this specific link that they are brought to a logon page where they can put their AD creds in and can then be sent to the page (that is displayed within sharepoint).

I believe the way to do this is to add an AD auth macro to my existing policy, but I can't figure out how to make it work only when that specific URI is called.