Multi-Step Authentication using ASDK

Hi,

we've implemented an authentication plugin for authenticating user to a third party authentication service.

The authentication is a two step process;  in the first step USER enters his username ; the plugin asks to the

third party authentication service which informations USER is required to provide to be able to authenticate ( may vary depening

on the user ) . based on the information received form the 3°party auth service, the plugin sends the user to the appropriate credential

collector page; once there the user enters the info he is asked for ; the plugin then authenticates the user.

There is now a requirement to authenticate users using the previously described mechanism BUT using the ASDK API; the problem i'm experiencing,