Yes, please checkout Setup DiscourseConnect - Official Single-Sign-On for Discourse (sso). This is the exact use case for Single Sign On.
With SSO though, you woudn’t need to invite them. They would just visit your discourse instance and be automatically logged in if they are already logged into your app. If they are not already logged into your app, discourse will redirect to your app for login, and then they will be auto-redirected back to discourse.