cloud function block create

gistfile1.txt

//only allow to sign up if the user exists on firestore.
const functions = require('firebase-functions');
const admin = require("firebase-admin");

admin.initializeApp();

exports.blockSignup = functions.auth.user().onCreate(user => {
    return new Promise((resolve, reject) => {
        admin.firestore().collection('users').doc(user.email).get().then(doc => {
            if (doc.exists) {
                resolve("letUserCreate");
            }
            else {
                reject(admin.auth().deleteUser(user.uid))
            }
        }).catch(reason => {
            console.error(reason)
            reject(admin.auth().deleteUser(user.uid))
        })
    });
});