I am developing an app for use with my SaaS application that has multiple instances used by customers around the world.  The initially login to app.6clicks.io which then, based on their location, redirects to app-us.6clicks.io, app-uk.6clicks.io, app-au.6clicks.io.  

We have an oauth2 identity provider which can be used with zapier no issue, but based on the different app locations and databases, need the redirect and access URL to be dynamically set (as well as then the api URL).

What’s the best way to do this?