ISA File Upload

We have to create application to upload a CSV file in SAP using a BAPI.

Our problem is that our customer ask us to include this functionaliti after log in operation of the user (internet user) in a standard ISA Application.

How we can manage user credential into our own jsp application ?

There is some functionality already available to upload the file into a BAPI in ISA application.

Thanks

Michele Truffelli