WordPress web service for authentication for outside program?

Been looking for plugins or any other way but can’t figure this out. I have a WordPress install and a custom desktop program. I need to log in to my desktop program using my WordPress users.

I’ve been looking everywhere for a plugin that provides a wordpress web service that takes a username and password and returns true or false basically. Should be simple.

I’m new to WordPress but have been programming for a while so if there is a tutorial somewhere for creating a plugin for this that should be fine also.

Thanks!