OAM Custom Authentication plugin issue

We are developing a custom authentication plugin for OAM11gR2 PS1. One of the requirement is to redirect to a external URL if user password has expired. As per the API documentation I am trying to get object of "GenericTransportContext" from AuthenticationContext object to get Transport handle and set authentication failure redirect URL. I am also referring Oracle provided sample authentication plugin which has same code. But this AuthenticationContext is always returing NULL for GenericTransportContext. I have attached both Oracle provided sample code and my custom code (line 203 always has null value for GenericTransportContext).
This custom plugin is used in an authentication module as second step in authentication modue, first step is out of box useridentification plugin.