How do I add a pattern to a role that I create using the Role Strategy API?

I'm using the Role Strategy API as found on here: https://wiki.jenkins.io/display/JENKINS/Role+Strategy+Plugin

I can add the roles correctly using the api. However, when I check via the UI, the role's pattern is ".*" meaning it matches with all the projects. However, I would like to grant specific roles to specific folders/jobs at the time of creation/update. How can I achieve this via the API? [I can create them perfectly well using the UI]