Secure HTTP trigger for Cloud Functions for Firebase

Question

Is there a way to check if a user is firebase-authorized before triggering a cloud function? (Or within the function)

Answer 1

Yes. You will need to send the Firebase ID token along with the request (for example in the Authorization header of an AJAX request), then verify it using the Firebase Admin SDK. There is an in-depth example in the Cloud Functions for Firebase samples repository. It looks something like this (made shorter for SO post):

const functions = require('firebase-functions');
const admin = require('firebase-admin');
const cors = require('cors')();

const validateFirebaseIdToken = (req, res, next) => {
  cors(req, res, () => {
    const idToken = req.headers.authorization.split('Bearer ')[1];
    admin.auth().verifyIdToken(idToken).then(decodedIdToken => {
      console.log('ID Token correctly decoded', decodedIdToken);
      req.user = decodedIdToken;
      next();
    }).catch(error => {
      console.error('Error while verifying Firebase ID token:', error);
      res.status(403).send('Unauthorized');
    });
  });
};

exports.myFn = functions.https.onRequest((req, res) => {
  validateFirebaseIdToken(req, res, () => {
    // now you know they're authorized and `req.user` has info about them
  });
});