Custom/external Customer Database?

[joachimm]

http://www.konakart.com/product/customization says:

"Use customers defined in another system. Many companies will already have customers defined in an existing system. KonaKart can be customized to interface to this external data source instead of using customer information directly from its own database."

I see how to customize the signon process to use our authentication system, but I don't see how to use an external customer database.

Can anyone give me a pointer to some information about this?  Is this accomplished with a custom implementation of a java API or just a SQL configuration change?

Thanks --Joachim