Is there a built-in event to listen to requests? I need to listen for a specific page and pull a variable from the query string for an add-on I'm building, but I don't see any Statamic or Laravel events that would suffice.

I'm working through a fairly complicated workflow where I have to redirect to a 3rd party site for OAuth authentication and then redirect back to my site to finish the process of subscribing a user (this is required by their API). They send a variable via the query string that I need to access in order to perform the rest of my logic. Is there another way to grab this data from within an add-on that I'm not thinking of?

P.S. I am a bit of a beginner with add-on building so I appreciate any help. Thanks!