I think the answer was right under my nose. In starting a post to Stackoverflow, I went to find the Auth0 Angular sample to provide as the code base. In doing so, I stumbled upon its sibling directory: https://github.com/auth0-samples/auth0-angular-samples/blob/master/02-Calling-an-API/src/app/services/api.service.ts
Out of time to comb through it now, but maybe it’ll help someone in the meanwhile.