APM External Logon Page return values

Hi,

Wondering if someone could clarify how to use an External Logon page and how to take input other than Username and password and use it to choose a path in the Access Policy

e.g. I would like a user to chose a specific Authentication method and then based on what they selected chose a path in the Access Policy...

External logon page -> Evaluate Selection made on Logon Page and choose path in Access Policy

How to do you use the values they entered in the External Logon page and then evaluate them once they are passed back???

Cheers