Hi Andrew,
Right now there is in fairly wide use an LDAP authentication module, and recently a shibboleth authentication module has been contributed but is yet in the main webwork code repository. (But you could probably use it if you want.) There's also one for "Cosign," but I think that may be specific to Michigan?
Unless you can use one of those protocols, you'll have to write your own authenication submodule. It shouldn't be too hard; maybe this would help:
http://search.cpan.org/~osalaun/AuthCAS-1.5/lib/AuthCAS.pm
Also, if you've got your CAS system already hooked up for Moodle (or, soon, Blackboard) you could use that as a frontend for WeBWorK and have it do the authentication.
Jason
WeBWorK Main Forum
CAS Authentication Setup
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