topt-generator using crypto-js library (for use in postman)

topt-generator.js

/*
Code borrowed from the following library and modified to work with crypto-js (for use in postman): 
	https://github.com/bellstrand/totp-generator/blob/master/LICENSE 

Install requirements:
	npm i crypto-js
Run: 
	node otp_script.js {{GOOGLE AUTH KEY}}
*/

let CryptoJS = require("crypto-js");

function hex2dec(s) {
	return parseInt(s, 16);
}

function dec2hex(s) {
	return (s < 15.5 ? '0' : '') + Math.round(s).toString(16);
}

function base32tohex(base32) {
	let base32chars = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ234567',
		bits = '',
		hex = '';

	base32 = base32.replace(/=+$/, '');

	for(let i = 0; i < base32.length; i++) {
		let val = base32chars.indexOf(base32.charAt(i).toUpperCase());
		if (val === -1) throw new Error("Invalid base32 character in key");
		bits += leftpad(val.toString(2), 5, '0');
	}

	for(let i = 0; i + 8 <= bits.length; i += 8) {
		let chunk = bits.substr(i, 8);
		hex = hex + leftpad(parseInt(chunk, 2).toString(16), 2, '0');
	}
	return hex;
}

function leftpad(str, len, pad) {
	if(len + 1 >= str.length) {
		str = Array(len + 1 - str.length).join(pad) + str;
	}
	return str;
}


function getToken(key, options) {
	options = options || {};	
	let epoch, time, shaObj, hmac, offset, otp;
	options.period = options.period || 30;
	options.algorithm = options.algorithm || 'SHA-1';
	options.digits = options.digits || 6;
	key = base32tohex(key);
	epoch = Math.round(Date.now() / 1000.0);
	time = leftpad(dec2hex(Math.floor(epoch / options.period)), 16, '0');
    	shaObj = CryptoJS.algo.HMAC.create(CryptoJS.algo.SHA1, CryptoJS.enc.Hex.parse(key));
   	shaObj.update(CryptoJS.enc.Hex.parse(time));
    	hmac =  shaObj.finalize().toString(CryptoJS.enc.Hex);
	offset = hex2dec(hmac.substring(hmac.length - 1));
	otp = (hex2dec(hmac.substr(offset * 2, 8)) & hex2dec('7fffffff')) + '';
	otp = otp.substr(otp.length - options.digits, options.digits);
	return otp;
}

console.log(getToken(process.argv[2]))