Review lnurl-auth compatibility with Zeus, Blixxt,...

[bumi]

Describe the bug LNURL-auth with LND does not generate the same key as Zeus.

To Reproduce Steps to reproduce the behavior:

1. Connect a LND node
   1. Visit stacker.news
   2. login with lightning
2. Use Zeus and connect the same LND
   1. Visit stacker.news
   2. login with lightning

Those should log you into the same account.

Expected behavior The lnurl-auth should create the same keys.

Information About Alby

• Alby Version: 1.10.0
• Alby installed through: Chrome store
• Wallet connected with Alby: LND

Further info:

• Code in Zeus: https://github.com/ZeusLN/zeus/blob/c0003371b125c378115219970428ee93365ac31c/views/LnurlAuth.tsx#L95-L129
• Code in Blixxt: https://github.com/hsjoberg/blixt-wallet/blob/f27afc779f2b0429743cf993f31155a1da88dd36/src/state/LNURL.ts#L314-L373
• Code in Alby: https://github.com/getAlby/lightning-browser-extension/blob/master/src/extension/background-script/actions/lnurl/auth.ts#L116
• Spec:
  https://github.com/fiatjaf/lnurl-rfc/blob/luds/13.md
• balance of satoshi:
  https://github.com/alexbosworth/balanceofsatoshis/blob/6d83d2c8ef133a0fad7fb89b067bb9f0dc8400be/lnurl/sign_auth_challenge.js#L34

[bumi]

There seems to be in issue with the hmac generation:

we use crypto.js hmacSHA256 zeus uses HMAC from fast-sha256

const hashingKey = '...'
//Alby
const AlinkingKeyPriv = hmacSHA256("getalby.com", hashingKey).toString(Hex);
console.log({ AlinkingKeyPriv });

//Zeus
const ZlinkingKeyPriv = new sha256HMAC(Buffer.from(hashingKey, "hex"))
  .update(stringToUint8Array("getalby.com"))
  .digest();
console.log({ ZlinkingKeyPriv });