Warp uses magic-wormhole.io and my android client uses the same domain for its Rendezvous and Transit servers. I am still learning about what they really are.
So I think the mentioned URLs might be closed source, I don’t know. But the default ones that warp use is this magic-wormhole.io (relay and transit) seems to be open source ones.
I have looked into how the firewall gets bypassed. To my knowledge they seems to be applying a method called firewall punch through in which the clients establish connection with each other using an external rendezvous server.