Creating custom fixture for FitNesse for Appian

Hello,

We want to use FitNesse scripts to test some custom SSO functionality as well as we have our test suites developed in Appian, we're well versed with Selenium with Java but didn't found any guide to create custom fixtures for FitNesse for Appian, can someone point us to right direction on how we can create those? Do we need to create custom JARS for it or something else? Any help is appreciated.

Thanks