I don't quite get how cloudflare do authentication. Is it just a diffie-hellman key exchange? And CF to generate millions of public-private key pairs like the g

I don't quite get how cloudflare do authentication. Is it just a diffie-hellman key exchange? And CF to generate millions of public-private key pairs like the good old CAs? What happens to devices with extremely limited storage space and computing power? One needs to use something like NaCl for key exchange and encryption afterall right? Can someone shed some light on this area? thanks!