MediaWiki 1.27 here, and Drupal as a CAS server. First of all, this extension lets the PHPCAS library muck directly with the PHP session. And it reuses CAS session ticket as an identifier of the PHP session. This fails validation in validateSessionId() as too short. After "fixing" the regexp, all this extension does is a few roundtrips to the CAS server. I am not logged in.
In my opinion, the extension must be archived, especially because its code is quite similar to Extension:CASAuthentication which is already archived.