So this is a bit of bikeshedding.  I like:
CAS_SESSION_EXPIRE_COOKIE_NOW
as a descriptor, since it forces the cookie expiration.

CAS_SESSION_EXPIRE_COOKIE_TIMEOUT

isn't as clear (I know I suggested the name before).  Maybe something like CAS_SESSION_EXPIRE_SESSION_SCOPE_TIMEOUT ?

to indicate that it's a session scoped cookie?