Firebase CronJobs - how to allow http triggers from one cronjob site

Since Firebase (Real-time DB) does not support cron-jobs I am using cron-job.org to schedule http triggers. This function should fire once at the end of every day, so at around 11:55pm. The thing is I would like only cron-job.org to be able to trigger the http endpoint and no one else (e.g. someone malicious trying to trigger it many times a day). How can I achieve this in my cloud function?

I have setup the cronjob and this is all the code I have right now:

exports.findAndDeleteSevenDayJobs = functions.https.onRequest((req, res) => {
  console.log('req',req);
});

Also, cron-job.org offers this:

And I have no idea how to use it.

To create cron-jobs in firebase RDB use a third party service like cron-job.org

1) CREATING THE KEY

To make everything secure you have to generate a secure key, from now on called YourSelfGeneratedButSecureKey.

You can generate one in your terminal by typing: node -e "console.log(require('crypto').randomBytes(20).toString('hex'))"

2) CREATING CRON JOB

Create a new cron-job that will hit your cloud function end-point and attach the created key as a url-query like so:

https://{projectSpecific}.cloudfunctions.net/{nameOfFunction}?key={YourSelfGeneratedButSecureKey}

Setup the key into your env by using the following command in your terminal: firebase functions:config:set cron.key="{YourSelfGeneratedButSecureKey}"

3) CLOUD FUNCTION

To make sure everything is maximum security you can install secure-compare by typing npm install --save secure-compare;

Then in your cloud function:

const secureCompare = require('secure-compare');

exports.{nameOfFunction} = functions.https.onRequest((req, res) => {

  const { key } = req.query;

  if (!secureCompare(key, functions.config().cron.key)) {
    console.log('Key in request and in env do NOT match');
    res.status(403).send('Security key does not match.');
    return null;
  }
  
  // DO REPETITIVE STUFF SECURELY 

});