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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def mk_auth_token(self, account, admin=False, duration=0):
 """ Builds an authentification token, using preauth mechanism. See http://wiki.zimbra.com/wiki/Preauth :param duration: in seconds defaults to 0, which means "use account default" :param account: an account object to be used as a selector :returns: the auth string """

        domain = account.get_domain()
        try:
            preauth_key = self.get_domain(domain)['zimbraPreAuthKey']
        except KeyError:
            raise DomainHasNoPreAuthKey(domain)
        timestamp = int(time.time())*1000
        expires = duration*1000
        return utils.build_preauth_str(preauth_key, account.name, timestamp,
                                       expires, admin)