sponsor using Express framework

sponsor.js

const express = require('express')
const cry = require('thor-devkit/dist/cry')
const Transaction = require('thor-devkit/dist/transaction').Transaction

const app = express()
app.use(express.json())
const port = 3000

app.post('/', function(req, res) {

    // Re-construct the transaction from the request.
    const tx = new Transaction(req.body['txBody'])
    // Extract 'sender' address from request.
    const sender = req.body['sender']

    // Compute the sponsor hash.
    const sponsorHash = tx.signingHash(sender)

    // Sponsor account (with money): 
    // 0x126cdb344f476f25b9fb2050513f425a82f71046
    const sponsorPriv = Buffer.from(
        '5df5e7f22a71dfd3d032ff5eb9dfc7dbe9c950e0671745826639a0423cd45d7f',
        'hex'
    )

    // Compute the sponsor signature with hash+private key.
    const signature = cry.secp256k1.sign(sponsorHash, sponsorPriv)

    // Send back the signature.
    res.send({
        'sponsor_signature': signature.toString('hex')
    })

})

app.listen(port, () => console.log(`Example app listening on port ${port}!`))