CoDWaW uses a particular demonware key for allowing clients to connect, it's all explained in detail in the following post:
post5232.html#p5232I have not continued the research because I don't have the game, anyway the only remaining part is how getting that 16 bytes hash of the server which I think is got when the client login in the demonware network.
as far as I know that hash doesn't change because it's built on the cdkey of the server so when the client knows it, he can joins the server when he wants, anyway that's all I know.