How to access application-level variables inside transform.js in VBCS?

Summary:

Unable to access app-level variables in transform.js to dynamically set request headers for all REST calls.

Content (please ensure you mask any confidential information):

I am trying to access an application-level variable inside transform.js in VBCS, but I could not find a supported or documented way to do this.

Based on a user selection in the web application, which sets an app-level variable, I need to dynamically pass its value as a HTTP request header in each and every REST call to the backend. This should happen for both dynamic calls made by SDP's and REST calls in action chains.