Github TOTP in Node.js

totp.ts

import { createHmac } from 'crypto';

// token here
const priv = "...";

const base32chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZ234567";
const base32tohex = (base32: string) => base32
    .toUpperCase()
    .replace(/=+$/, "")
    .split('')
    .map(char => {
        const val = base32chars.indexOf(char);
        if (val === -1) {
            throw new Error(`Incorrect character: ${JSON.stringify(char)}`)
        }
        const bits = val.toString(2).padStart(5, '0');
        return bits;
    })
    .join('')
    .match(/.{1,8}/g)
    .map(chunk => parseInt(chunk, 2).toString(16).padStart(2, "0"))
    .join('');

type Options = Partial<{
    period: number,
    digits: number,
    timestamp: number,
}>

const hex2dec = (s: string) => parseInt(s, 16);

const mask31bit = hex2dec("7fffffff");

const getToken1 = (key: string, {
    period = 30,
    digits = 6,
    timestamp = Date.now(),
}: Options = {}) => {
    const kkey = base32tohex(key);
    const secondsSinceEpoch = Math.floor(timestamp / 1000.0);
    const time = Math.floor(secondsSinceEpoch / period)
        .toString(16)
        .padStart(16, "0");
	const hmac = createHmac('sha1',  Buffer.from(kkey, 'hex'))
        .update(Buffer.from(time, 'hex'))
        .digest('hex');
    // takes the 4 least significant bits of the MAC and uses them as a byte offset i
	const offset = hex2dec(hmac.substring(hmac.length - 1));
    // index i is used to select 31 bits from MAC, starting at bit i × 8 + 1:
	const otp = String(hex2dec(hmac.substr(offset * 2, 8)) & mask31bit);
	return otp.substr(Math.max(otp.length - digits, 0), digits);
}

console.log(getToken1(priv, {
	digits: 6,
	period: 30,
}));