Code for checksum and transaction verification

verifyTransaction.js

let callbackResponse = ''

req.on('error', (err) => {
    console.error(err.stack)
}).on('data', (chunk) => {
    callbackResponse += chunk
}).on('end', () => {
    let data = qs.parse(callbackResponse)
    console.log(data)

    data = JSON.parse(JSON.stringify(data))

    const paytmChecksum = data.CHECKSUMHASH

    var isVerifySignature = PaytmChecksum.verifySignature(data, PaytmConfig.PaytmConfig.key, paytmChecksum)
    if (isVerifySignature) {
        console.log("Checksum Matched");

        var paytmParams = {};

        paytmParams.body = {
            "mid": PaytmConfig.PaytmConfig.mid,
            "orderId": data.ORDERID,
        };

        PaytmChecksum.generateSignature(JSON.stringify(paytmParams.body), PaytmConfig.PaytmConfig.key).then(function (checksum) {
            paytmParams.head = {
                "signature": checksum
            };

            var post_data = JSON.stringify(paytmParams);

            var options = {

                /* for Staging */
                hostname: 'securegw-stage.paytm.in',

                /* for Production */
                // hostname: 'securegw.paytm.in',

                port: 443,
                path: '/v3/order/status',
                method: 'POST',
                headers: {
                    'Content-Type': 'application/json',
                    'Content-Length': post_data.length
                }
            };

            // Set up the request
            var response = "";
            var post_req = https.request(options, function (post_res) {
                post_res.on('data', function (chunk) {
                    response += chunk;
                });

                post_res.on('end', function () {
                    console.log('Response: ', response);
                    res.write(response)
                    res.end()
                });
            });

            // post the data
            post_req.write(post_data);
            post_req.end();
        });
    } else {
        console.log("Checksum Mismatched");
    }
})