@justinfox,
There are a few ways in which you can architect this to ensure the user/entity is authenticated and authorized (reader here) depending on the language and architecture used. The tutorials and guides cover a few different approaches.
https://fusionauth.io/learn/expert-advice/authentication/login-authentication-workflows/ offers a high-level overview as well.
Lastly, if you decide to use OAuth, you could consult our modern guide to OAuth for more information.
https://fusionauth.io/learn/expert-advice/oauth/modern-guide-to-oauth/
Thanks,
Josh