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import { createHmac } from "node:crypto";
const getHMAC = (k,c) => { const h = createHmac("sha1", k);
h.update(c, "hex"); return h.digest("hex"); }
const h2d = s => parseInt(s, 16);
const d2h = s => Math.floor(s).toString(16).padStart(2,0);
const b32a = "ABCDEFGHIJKLMNOPQRSTUVWXYZ234567";
const b32u = s => Uint8Array.from(s.split("").reduce((a,c) =>
a+b32a.indexOf(c.toUpperCase()).toString(2).padStart(5,0), "")
.match(/.{8}/g).map(b => parseInt(b,2)));
export default function totp(secret, { expiry=30,
now=Math.round(new Date().getTime()/1000), length=6 }={}) {
const time = d2h(now/expiry).padStart(16,0);
const hmac = getHMAC(b32u(secret), time);
const offset = h2d(hmac.substring(hmac.length - 1));
const otp = (h2d(hmac.substr(2*offset, 8)) & h2d("7fffffff")) + "";
return otp.padStart(length,0).substr(-length);
}
export function check(token, secret, { expiry=30,
now=Math.round(new Date().getTime()/1000), length=6, window=0 }={}) {
const i = Array(window*2+1).fill().map((e,i) => now+(expiry*(i-window)))
.findIndex(n => token === this(secret, {now:n, expiry, length}));
return i>=0 && i-window;
}
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