I have a mobile app with a backend hosted on firebase. I also have several services that a hosted on digitalocean. There services are only meant to be called from firebase functions and should not be accessed directly. What would be the best way achieve this level of security? I know that firebase functions does not have a fixed ip address so whitelisting ips will not work.

I’m thinking of using a basic http authentication between firebase functions and digitalocean server… Is there a better option?