Permissions Error with Cloud Function Adding Data to Firestore - firebase

Question

I'm trying to setup a Cloud Function that, when ran by Cloud Scheduler, will insert certain data into my Firestore Database. I am doing this in Node.js using the Inline editor provided when creating my Cloud Function.
I keep getting the error:
"Error: function crashed. Details:
7 PERMISSION_DENIED: Missing or insufficient permissions."
On my Firebase dashboard, the logs show my function and the error that I get when I test my Cloud Function, so I'm assuming my function is hitting the database, just not adding the dummy data I was testing with.
index.js:
const Firestore = require('#google-cloud/firestore');
const PROJECTID = 'MY_PROJECT_ID';
const firestore = new Firestore({
projectId: PROJECTID,
timestampsInSnapshots: true,
});
/**
* Responds to any HTTP request.
*
* #param {!express:Request} req HTTP request context.
* #param {!express:Response} res HTTP response context.
*/
exports.helloWorld = (req, res) => {
return firestore.collection("users").add({
first: "Ada",
last: "Lovelace",
born: 1815
});
};
Package.json:
{
"name": "sample-http",
"version": "0.0.1",
"dependencies": {
"#google-cloud/firestore": "0.17.0",
"semver": "^5.5.1"
}
}
I also have my rules set for my database as:
service cloud.firestore {
match /databases/{database}/documents {
match /{document=**} {
allow read, write;
}
}
}

Answer 1

Thanks to #andresmijares I was able to fix my problem. I looked more into the quickstart and changed my index.js as follows (specifically everything before the helloWorld function).
const admin = require('firebase-admin');
admin.initializeApp({
credential: admin.credential.applicationDefault()
});
const db = admin.firestore();
/**
* Responds to any HTTP request.
*
* #param {!express:Request} req HTTP request context.
* #param {!express:Response} res HTTP response context.
*/
exports.helloWorld = (req, res) => {
/* let message = req.query.message || req.body.message || 'Hello World!';
res.status(200).send(message);
*/
return db.collection("users").add({
first: "Ada",
last: "Lovelace",
born: 1815
});
};
And I got the error
"Code in file index.js can't be loaded. Did you list all required modules in the package.json dependencies? Detailed stack trace: Error: Cannot find module 'firebase-admin'"
Which I was able to fix by adding the 'firebase-admin' dependency into my package.json, as follows:
{
"name": "sample-http",
"version": "0.0.1",
"dependencies": {
"semver": "^5.5.1",
"#google-cloud/firestore": "^1.3.0",
"firebase-admin": "^7.1.1"
}
}
This was also all done in the inline editor provided when creating my Cloud Function, so no installation of anything was needed.

Answer 2

you need to download the sdk key, this is a json file that you can export from your firebase console Project Overview -> Project Settings -> Services Accounts
Then you can instantiate it like this:
var admin = require("firebase-admin");
var serviceAccount = require("path/to/serviceAccountKey.json");
admin.initializeApp({
credential: admin.credential.cert(serviceAccount)
});
When using the firebase admin sdk, the firestore security rules do not apply (they are only for client-side operations)