How to use the cookie-signature.unsign function in cookie-signature

if (!callback) {
    promise = new Promise(function(res, rej) {
      callback = function(err, result) {
        err ? rej(err) : res(result)
      }
    })
  }

  // read dynamo session table
  let name = process.env.SESSION_TABLE_NAME || 'arc-sessions'
  let secret = process.env.ARC_APP_SECRET || process.env.ARC_APP_NAME || 'fallback'
  // TODO: uppercase 'Cookie' is not the header name on AWS Lambda; it's
  // lowercase 'cookie' on lambda...
  let jar = cookie.parse(request.headers && request.headers.Cookie? request.headers.Cookie || '': '')
  let sesh = jar.hasOwnProperty('_idx')
  let valid = unsign(jar._idx || '', secret)

  // find or create a new session
  let exec = sesh && valid? find.bind({}, name) : create.bind({}, name)
  let params = sesh && valid? valid : {}

  exec(params, callback)
  return promise
}

const config = new Config()
      config.set('app.appKey', SECRET)
      const response = new Response(new Request(req, res), config)
      response.cookie('cart_total', '20')
      response.send('')
      response.end()
    })

    const { headers } = await supertest(server).get('/').expect(200)
    const encrypter = simpleEncryptor({
      key: SECRET,
      hmac: false
    })

    assert.strictEqual(
      sig.unsign(
        encrypter.decrypt(querystring.unescape(headers['set-cookie'][0].replace('cart_total=', ''))).replace('s:', ''),
        SECRET
      ),
      '20'
    )
  })

Object.keys(obj).forEach((function (key) {
  _$jscoverage['utils.js'][187]++;
  var val = obj[key];
  _$jscoverage['utils.js'][188]++;
  if (0 == val.indexOf("s:")) {
    _$jscoverage['utils.js'][189]++;
    val = signature.unsign(val.slice(2), secret);
    _$jscoverage['utils.js'][190]++;
    if (val) {
      _$jscoverage['utils.js'][191]++;
      ret[key] = val;
      _$jscoverage['utils.js'][192]++;
      delete obj[key];
    }
  }
}));
  _$jscoverage['utils.js'][196]++;

exports.parseSignedCookie = function(str, secret){
  return 0 == str.indexOf('s:')
    ? signature.unsign(str.slice(2), secret)
    : str;
};

exports.parseSignedCookie = function(str, secret){
  return 0 == str.indexOf('s:')
    ? signature.unsign(str.slice(2), secret)
    : str;
};

exports.parseSignedCookie = function(str, secret){
  return 0 == str.indexOf('s:')
    ? signature.unsign(str.slice(2), secret)
    : str;
};

exports.parseSignedCookie = function(str, secret){
  return 0 == str.indexOf('s:')
    ? signature.unsign(str.slice(2), secret)
    : str;
};

function unsigncookie(val, secrets) {
  for (var i = 0; i < secrets.length; i++) {
    var result = signature.unsign(val, secrets[i]);

    if (result !== false) {
      return result;
    }
  }

  return false;
}

exports.parseSignedCookie = function(str, secret){
  return 0 == str.indexOf('s:')
    ? signature.unsign(str.slice(2), secret)
    : str;
};

Object.keys(obj).forEach(function(key){
    var val = obj[key];
    if (0 == val.indexOf('s:')) {
      val = signature.unsign(val.slice(2), secret);
      if (val) {
        ret[key] = val;
        delete obj[key];
      }
    }
  });
  return ret;