I need to defend against receiving a massive spam of UDP packets from random spoofed IP addresses. I would make it this way:
In my protocol, every UDP packet contains username and password. Firewall(3rd party) would have updatable list of users(name and password). It would check if packet contains valid data, if yes then it would pass it to my server, if not, then my bandwidth would be not affected.
My question is, do you know any service that would allow such solution?