Use Firebase Cloud Functions to call a method from both callable and http requests

index.js

function callMeAnywhere(uid, foo) {
   if( !uid ) throw new Error("Must authenticate");
   return foo + 'bar';
}

functions.https.onCall((data, context) => {
  const data = callMeAnywhere(context.auth.uid, data.foo);
  return {data: data};
})

// Use this with https://github.com/firebase/functions-samples/tree/master/authorized-https-endpoint
app.get('/foo', (req, res) => {
  const data = callMeAnywhere(req.user.id, req.params.foo);
  res.send(data);
});
functions.https.onRequest(app);