> Your whitelist will end up looking like "All of Azure, GCP, AWS, and CloudFlare, plus some one-offs"...
Why?
Why?
* A huge-ass slice of the things hosted on The Internet are hosted in or behind one or more of Azure, GCP, AWS, and CloudFlare.
* Recording the set of "cloud provider"-provided IP addresses spoken to by a piece of client software is a bit of a fool's errand. The nature of those services is that one can change the IP address assigned to one's deployed software at a whim... and it's often cheaper to set things up so that one doesn't have an IP address for one's services that survives a VM reboot.