I'm taking the first step in bringing a classic-ASP app into the 21st century, replacing the existing authentication with fusionauth.

Welcome! 🙂

Once I've added google as a social auth provider and a user attempts to login, the google authentication part happens (user is sent to google and logs in there), but then I'm just stuck on the screen below... never redirected to the redirect_uri or anything.

Hmmm. That's curious. Is there any information about the error in the event log or log tabs (under system)?

What version of FusionAuth are you running?

Also, i noticed if user clicks on create an account it goes to the registration page, which doesn't have a register with google link, even though I've enabled that "create registration" flag in the google settings for my application.

So if you enable "create registration" that means that a user can authenticate with google and then be automatically registered for the given FusionAuth application. This means they'll be authorized to access that application (and receive a 200 when authenticating against it).

This doesn't mean that a user can sign up with google from your application. More details here: https://fusionauth.io/docs/v1/tech/identity-providers/