Looking for registration package

[kj]

I'm looking for a Python-based, small, self-contained package to
hand out API keys, in the same spirit as Google API keys.

The basic specs are simple: 1) enforce the "one key per customer"
rule; 2) be robot-proof; 3) be reasonably difficult to circumvent
even for humans.

(This is for a web service we would like to implement; the goal is
to be able to control the load on our servers.  Therefore, if the
package includes an automated log-analysis component, all the
better, but this is not necessary.)

Any suggestions would be appreciated.

Thanks!

~K