WepAPI v2 running in local host trying to register test user

I have an angular 4 cordova app using Auth0. I have it implemented, and users can register, log in and out. I am now trying to figure out how to set up a test bed with a C# Web API v2 back end running on a localhost port. I see that there is a rule “Custom webhook with ASPNET WebApi2” that can call this api so that I can register a user and return their internal ID.
Before even doing this I notice I have no details from Auth0 that identify who the user is that logged in, so I assume I need to use this hook so that the internal ID can be established with each login. Every time that rule fires against localhost:1234 it just says connection refused, which makes sense because it seems the call is being made from Auth0 and they cannot access my local instance.
The question is, do I have to publish a minimal api to have that functionality work, even though I will be building the api locally for my app to fire against? What is the best approach here for setting up this minimal scenario?