authenticity_token doesn't work on host mapped helpcenter

Unfortunately, the authenticityToken solution provided in the below article doesn't work if your helpcenter is host mapped. I get a 403 error message and support have confirmed that it's an issue. My use case requires the token in order to make api calls to the subscription endpoint for users logged into the helpcenter.

https://developer.zendesk.com/apps/docs/help-center-templates/v1

For those who were stuck, there's an undocumented way of getting it. If you make a call to /hc/api/internal/csrf_token.json, you'll be able to access an object containing current_session_csrf_token. This token will work on host mapped helpcenters. It's undocumented so be prepared for it to disappear at some point in the future.