Transactions.js

const Web3 = require('web3');
const web3js = new  Web3(Web3.givenProvider || 'https://ropsten.infura.io/VOTRE_ACCES_INFURA', null, {});
const Tx = require('ethereumjs-tx');
const express = require('express');
const router = express.Router();
const BigNumber = require('bignumber.js');

var contractABI = CODE_ABI_DE_VOTRE_TOKEN

contractAddress = "ADRESSE_DU_CONTRAT_DE_VOTRE_TOKEN";

let makeTransaction = (fromAdresse, toAdresse, amount) => {
    var tokenContract = new web3js.eth.Contract(contractABI, contractAddress);
    var myAddress = 'VOTRE_ADRESSE';
    var privateKey = Buffer.from('VOTRE_CLE_PRIVEE', 'hex')
    var count;

    return new Promise ((res, rej) => {
        if (!fromAdresse || !toAdresse || !amount){
            return res({
                message: 'You must send all datas'
            });
        }

        return web3js.eth.getTransactionCount(myAddress)
        .then(function(c){
            count = c;
            hexamount = web3js.utils.toHex(amount * DECIMALS_DE_VOTRE_TOKEN);
            var rawTransaction = {"from":myAddress, "gasPrice":web3js.utils.toHex(20 * 1e9),"gasLimit":web3js.utils.toHex(210000),"to":contractAddress,"value":"0x0","data":tokenContract.methods.transfer(toAdresse, hexamount).encodeABI(),"nonce":web3js.utils.toHex(count)}
            var transaction = new Tx(rawTransaction);
            transaction.sign(privateKey);

            web3js.eth.sendSignedTransaction('0x'+transaction.serialize().toString('hex'))
            return res({
                message: "transaction from " + myAddress + " to " + toAdresse + " of " + amount + " done !"
            });
        })
        .catch(error => {
            console.log('caught', error.message);
        });
    });
};

router.post("/sendtx", (req, res) => {
    var myAddress = 'VOTRE_ADDRESSE';
    var privateKey = Buffer.from('VOTRE_CLE_PRIVEE', 'hex')

    makeTransaction(myAddress, req.body.to, req.body.amount)
    .then(transaction => {
        res.send({
            success: true,
            message: transaction.message
        });
    })
    .catch(err => {
        console.log("error");
        res.send(
            {
                success: false,
                err: err.message
            });
    });
});

module.exports = router;