OAuth2's place in activitypub server apps

I am having a bit of trouble understanding how to implement OAuth in the web app I am creating,
so I am wondering if you know of any resources that explains how to add OAuth support to a activitypub server app, without being dependent on external services in the context of authenticating users and/or client apps, if you know of any the rust programming language that would be amazing as I am creating my project in rust but any resource that helps to simplify OAuth in the context of authenticating users and/or client apps is helpful