Firebase Callable Function + CORS

I'm trying to call a callable Cloud Function from my app, but I'm facing CORS issues.

I can't enable Cors since I don't have access to the request and response on the onCall function. This is my function:

exports.UserInvitation = functions.https.onCall((data, context) => {
  const email = data.email


  return new Promise((resolve, reject) => {
    admin.auth().createUser({
      email: email,
      emailVerified: false,
      password: password
    }).then(resolve).catch((err) => {
      console.error(err.code)
      reject(new functions.https.HttpsError(err.code, err.message))
    })
  })
})

And this is how I call it:

functions.httpsCallable('UserInvitation')({ email: this.input.value }).then((data) => {
      console.log('Sent invitation:', data)
})

Firebase-functions package.json:

{
  "name": "functions",
  "description": "Cloud Functions for Firebase",
  "scripts": {
    "serve": "firebase serve --only functions",
    "shell": "firebase functions:shell",
    "start": "npm run shell",
    "deploy": "firebase deploy --only functions",
    "logs": "firebase functions:log"
  },
  "dependencies": {
    "bluebird": "^3.5.1",
    "firebase-admin": "~5.12.0",
    "firebase-functions": "^1.0.1"
  },
  "private": true
}

WEB SDK Firebase version: 4.13.1

For anybody else who has arrived here searching firebase callable functions cors errors, here's my checklist:

1. Ensure the function is deployed.
2. Ensure the function name is correct. I was calling recalculatY when it should have been recalculateY. Got a cors error for some reason.
3. Ensure the function code itself is not throwing an error. Use the emulator to help. This didn't throw a cors error still helpful to know.
4. Ensure your regions match - I am using europe-west2. I had to both deploy the function with that region, and call it using the region. For a while, I assumed the client would infer the correct region if the function name was correct. That was not the case.

Deploying a callable function to a specific region:

// This is the file in which you define your callable function.
const functions = require('firebase-functions');
...
exports.yourFunc = functions.region('europe-west2').https.onCall(async (data, context) => {
    ...
})

Calling a function in a specific region from the client (in this case, a vuejs web app):

// In my case, this is a vuex store file, but it is safe to assume this is plain old javascript
import firebase from 'firebase/app'
import 'firebase/functions'
...
firebase.app().functions('europe-west2').httpsCallable('yourFunc')

Note: firebase.app().function... vs firebase.app.function...

For anyone looking at this post Jan 2020..

Found this answer on Reddit (https://www.reddit.com/r/reactjs/comments/fsw405/firebase_cloud_functions_cors_policy_error/)

Turns out on 15th Jan 2020, Google changed the security settings where all new functions no longer have a Cloud Functions Invoker. This means that all newly created functions will have their access forbidden, thus resulting in a CORS policy block.

Here is how you fix it, as it's not all that obvious:

https://cloud.google.com/functions/docs/securing/managing-access-iam#allowing_unauthenticated_function_invocation