Writing a secure client/server with open source

[edA-qa mort-ora-y]

I am writing a score server for client/server games such that various
games can talk to one server.  Each game would thus register for a
name/password and use that in their code to send data to the server.

Now, putting aside all the problems with cheat detection found in closed
source software, it seems my problem is exacerbated by the need to
distribute full code to make the client (this will be the AGPL so server
code is also included).

Does anybody have some good references, or good ideas, on how this can
be accomplished, such that each game client can uniquely identify itself
with the server?  That is, how can I adequately protect some "keys" in a
completely AGPL project?

NOTE: I already understand the problem with detecting cheaters, and I
realize this is a part of the same problem.  I'm just hoping that
somebody has an idea that the most basic identity of a game client can
be protected.

-- 
edA-qa mort-ora-y
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