Letting authorized users add or change categories on the front end

I’ve been playing around with using a password protected WordPress install as a content management system. I’d like to be able to add a function to the front end where an authorized user can add a category to a post via one click* – without having to go to the dashboard.

I found a thread that showed how to delete a post on the front end and that worked fine. Adding a category is a bit beyond my skill set.

Thanks for taking the time to read this.

(*Adding the category “completed” for a to do list so I can restrict it from showing up on the main page.)