def create_ticket_str(self, prefix=None):
        """
        Generate a sufficiently opaque ticket string to ensure the ticket is
        not guessable. If a prefix is provided, prepend it to the string.
        """
        if not prefix:
            prefix = self.model.TICKET_PREFIX
        return "%s-%d-%s" % (prefix, int(time.time()),
                             get_random_string(length=self.model.TICKET_RAND_LEN))