'Verifies the expiry date of the object\'s issue date.
If the expiry date is not yet reached and the protocol state is still
valid, `True\' is returned.  If the protocol state has expired, `False\'
is returned.'

def isValid(self):

    assert self.issueDate
    lifetime = (int(time.time()) - self.issueDate)
    if (lifetime > const.SESSION_TICKET_LIFETIME):
        log.debug(('The    ticket    is    invalid    and    expired    %s    ago.' % str(datetime.timedelta(seconds=(lifetime - const.SESSION_TICKET_LIFETIME)))))
        return False
    log.debug(('The    ticket    is    still    valid    for    %s.' % str(datetime.timedelta(seconds=(const.SESSION_TICKET_LIFETIME - lifetime)))))
    return True
