1 files changed, 79 insertions, 0 deletions
diff --git a/src/lnurl.js b/src/lnurl.js
index 3f1b39b..bfebf0d 100644
--- a/src/lnurl.js
+++ b/src/lnurl.js
@@ -11,6 +11,10 @@
 // that broadcasts the receipt; we only sign the request.
 
 import { bech32 } from '@scure/base';
+import { secp256k1 } from '@noble/curves/secp256k1';
+import { hmac } from '@noble/hashes/hmac';
+import { sha256 } from '@noble/hashes/sha256';
+import { bytesToHex, hexToBytes } from '@noble/hashes/utils';
 import { parseNostrPubkey } from './nostr.js';
 
 const enc = new TextEncoder();
@@ -43,6 +47,9 @@ export function lnAddressToUrl(addr) {
 export function parseZapTarget(input, { pk = null } = {}) {
   const s = (input || '').trim().replace(/^lightning:/i, '');
   if (!s) return null;
+  // LUD-17: lnurlp:// (pay) and lnurlw:// (withdraw) are the URL itself over https (http on an onion)
+  const scheme = /^(lnurlp|lnurlw):\/\/(.+)$/i.exec(s);
+  if (scheme) { const url = (/^[^/]+\.onion(\/|$)/i.test(scheme[2]) ? 'http://' : 'https://') + scheme[2]; return { kind: 'lnurl', url, lnurlBech32: safeEncode(url), pk }; }
   // An npub/hex pubkey — the caller resolves lud16/lud06 from the profile and
   // calls fromProfile() below; here we just report the shape.
   const npk = parseNostrPubkey(s);
@@ -92,10 +99,14 @@ async function fetchJson(url, ms = 8000) {
 }
 
 // GET the LNURL-pay params. Normalizes the bits we use; keeps `callback`.
+// An lnurl that turns out to be a withdraw (LUD-03) is not an error here:
+// the thrown error carries its terms (`withdraw`) for the caller to take up.
 export async function fetchPayParams(url) {
   const d = await fetchJson(url);
   if (!d || d.tag !== 'payRequest' || !d.callback) {
     if (d && d.status === 'ERROR') throw new Error(d.reason || 'LNURL error');
+    const w = withdrawParamsOf(d);
+    if (w) { const e = new Error('a Lightning withdraw, not a payment'); e.withdraw = w; throw e; }
     throw new Error('not a Lightning pay endpoint');
   }
   return {
@@ -134,3 +145,71 @@ export async function requestInvoice(params, { amountMsat, zapRequest = null, ln
   if (!d.pr || typeof d.pr !== 'string') throw new Error('no invoice returned');
   return d.pr;
 }
+
+// ---- LNURL-auth (LUD-04): a login challenge, not a payment ----
+// An lnurl whose URL carries tag=login and a 32-byte k1. Pasted into Send
+// and taken for a payment, their server answered "no sig query variable
+// provided" (Stacker News, 2026-10-16). action: login | register | link | auth.
+export function parseLnurlAuth(input) {
+  const s = (input || '').trim().replace(/^lightning:/i, '');
+  if (!/^lnurl1[ac-hj-np-z02-9]+$/i.test(s)) return null;
+  let url;
+  try { url = new URL(decodeLnurl(s)); } catch { return null; }
+  if (url.searchParams.get('tag') !== 'login') return null;
+  const k1 = (url.searchParams.get('k1') || '').toLowerCase();
+  if (!/^[0-9a-f]{64}$/.test(k1)) return null;
+  const action = /^(register|login|link|auth)$/.test(url.searchParams.get('action') || '') ? url.searchParams.get('action') : 'login';
+  return { url: url.href, domain: url.hostname, k1, action };
+}
+// The linking key for a domain (LUD-05): from the wallet's master key,
+// m/138'/0 is the hashing key; its HMAC-SHA256 of the domain, read as four
+// 32-bit numbers, names the path m/138'/<n1>/<n2>/<n3>/<n4>. The same
+// wallet is the same user on a site, every time, and a different one on
+// every other site.
+export function lnurlAuthKey(master, domain) {
+  const hashing = master.derive("m/138'/0").privateKey;
+  const mac = hmac(sha256, hashing, new TextEncoder().encode(domain));
+  const dv = new DataView(mac.buffer, mac.byteOffset, 16);
+  let key = master.derive("m/138'");
+  for (const o of [0, 4, 8, 12]) key = key.deriveChild(dv.getUint32(o));
+  return key;
+}
+// Sign the challenge (ECDSA over k1, DER-encoded) and call the URL back with
+// sig and key. Resolves on the server's OK; throws its reason otherwise.
+export async function lnurlAuthLogin(auth, key) {
+  const sig = secp256k1.sign(hexToBytes(auth.k1), key.privateKey);
+  const url = new URL(auth.url);
+  url.searchParams.set('sig', sig.toDERHex());
+  url.searchParams.set('key', bytesToHex(key.publicKey));
+  const d = await fetchJson(url.href);
+  if (!d || String(d.status || '').toUpperCase() !== 'OK') throw new Error((d && d.reason) || 'login refused');
+  return { key: bytesToHex(key.publicKey) };
+}
+
+// ---- LNURL-withdraw (LUD-03): the other side asks to PAY us ----
+// Their terms: an amount range (msat), a callback and k1. We make an invoice
+// for the amount chosen and hand it to the callback; they pay it.
+export function withdrawParamsOf(d) {
+  if (!d || d.tag !== 'withdrawRequest' || !d.callback || !d.k1) return null;
+  const min = Math.max(0, Number(d.minWithdrawable) || 0), max = Number(d.maxWithdrawable) || 0;
+  if (!(max > 0)) return null;
+  let domain = '';
+  try { domain = new URL(d.callback).hostname; } catch {}
+  return { callback: d.callback, k1: String(d.k1), minMsat: min, maxMsat: Math.max(min, max), description: String(d.defaultDescription || '').slice(0, 200), domain };
+}
+export async function fetchWithdrawParams(url) {
+  const d = await fetchJson(url);
+  const w = withdrawParamsOf(d);
+  if (!w) { if (d && d.status === 'ERROR') throw new Error(d.reason || 'LNURL error'); throw new Error('not a Lightning withdraw'); }
+  return w;
+}
+// Hand them the invoice to pay. Their OK means they have it, not that it is paid.
+export async function submitWithdraw(params, invoice) {
+  const url = new URL(params.callback);
+  url.searchParams.set('k1', params.k1);
+  url.searchParams.set('pr', invoice);
+  const d = await fetchJson(url.href);
+  if (!d || String(d.status || '').toUpperCase() !== 'OK') throw new Error((d && d.reason) || 'withdraw refused');
+  return true;
+}
+