code: function touch(token, cb) {
    var date = stampify(conf.session_maxage);
    db.getClient(function(err, client, done) {
      client.query("UPDATE tokens SET expires_at = $1 WHERE token = $2", [date, token], function() {
        cb.apply(null, arguments);
        done();
      });
    });
  }
docs: Touch token, set its `token.expires_at` to Date.now() + conf.session_maxage