auth.go

package lnurl

import (
	"encoding/hex"
	"errors"
	"net/url"

	"github.com/btcsuite/btcd/btcec/v2"
	"github.com/btcsuite/btcd/btcec/v2/ecdsa"
)

type LNURLAuthParams struct {
	Tag         string   `json:"tag"`
	K1          string   `json:"k1"`
	Callback    string   `json:"callback"`
	CallbackURL *url.URL `json:"-"`
	Host        string   `json:"host"`
}

func (_ LNURLAuthParams) LNURLKind() string { return "lnurl-auth" }

// VerifySignature takes the hex-encoded parameters passed to an lnurl-login endpoint and verifies
// the signature against the key and challenge.
func VerifySignature(k1, sig, key string) (ok bool, err error) {
	bk1, err1 := hex.DecodeString(k1)
	bsig, err2 := hex.DecodeString(sig)
	bkey, err3 := hex.DecodeString(key)
	if err1 != nil || err2 != nil || err3 != nil {
		return false, errors.New("Failed to decode hex.")
	}

	pubkey, err := btcec.ParsePubKey(bkey)
	if err != nil {
		return false, errors.New("Failed to parse pubkey: " + err.Error())
	}

	signature, err := ecdsa.ParseDERSignature(bsig)
	if err != nil {
		return false, errors.New("Failed to parse signature: " + err.Error())
	}

	return signature.Verify(bk1, pubkey), nil
}

func HandleAuth(rawurl string, parsed *url.URL, query url.Values) (LNURLParams, error) {
	k1 := query.Get("k1")
	if _, err := hex.DecodeString(k1); err != nil || len(k1) != 64 {
		return nil, errors.New("k1 is not a valid 32-byte hex-encoded string.")
	}

	return LNURLAuthParams{
		Tag:         "login",
		K1:          k1,
		Callback:    rawurl,
		CallbackURL: parsed,
		Host:        parsed.Host,
	}, nil
}