As an alternative to the native Shishi programming API, it is possible to program Shishi through the Generic Security Services (GSS) API. The advantage of using GSS-API in your security application, instead of the native Shishi API, is that it will be easier to port your application between different Kerberos 5 implementations, and even beyond Kerberos 5 to different security systems, that support GSS-API. In the free software world, however, almost the only widely used security system that supports GSS-API is Kerberos 5, so the last advantage is somewhat academic. But if you are porting applications using GSS-API for other Kerberos 5 implementations, or want a more mature and stable API than the native Shishi API, you may find using Shishi's GSS-API interface compelling. Note that GSS-API only offer basic services, for more advanced uses you must use the native API.
Since the GSS-API is not specific to Shishi, it is distributed independently from Shishi. Further information on the GSS project can be found at http://www.gnu.org/software/gss/.