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// Copyright 2026 Rose Hogenson <r@roseh.moe>
//
// This file is part of roseh.moe.
//
// roseh.moe is free software: you can redistribute it and/or modify it
// under the terms of the GNU Affero General Public License as published
// by the Free Software Foundation, either version 3 of the License,
// or (at your option) any later version.
//
// roseh.moe is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty
// of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Affero General Public License for more details.
//
// You should have received a copy of the GNU Affero General Public
// License along with roseh.moe. If not, see
// <https://www.gnu.org/licenses/>.
package auth
import (
"bytes"
"crypto"
"crypto/ecdsa"
"crypto/hmac"
"crypto/rand"
"crypto/rsa"
"crypto/sha256"
"crypto/x509"
"encoding/base64"
"encoding/json/v2"
"fmt"
"io"
"log"
"net/url"
"slices"
"strings"
"sync"
"time"
"unicode"
)
var SecretKey []byte
func MAC(msg []byte, purpose string) []byte {
mac := hmac.New(sha256.New, SecretKey)
io.WriteString(mac, purpose)
io.WriteString(mac, ":")
mac.Write(msg)
return mac.Sum(nil)
}
func SignMsg(msg, purpose string) string {
return msg + base64.RawURLEncoding.EncodeToString(MAC([]byte(msg), purpose))
}
func VerifyHMAC(signedMsg, purpose string) (string, bool) {
macSize := base64.RawURLEncoding.EncodedLen(sha256.Size)
if len(signedMsg) < macSize {
return "", false
}
msg, msgMAC := signedMsg[:len(signedMsg)-macSize], signedMsg[len(signedMsg)-macSize:]
expectedMAC := base64.RawURLEncoding.EncodeToString(MAC([]byte(msg), purpose))
if !hmac.Equal([]byte(msgMAC), []byte(expectedMAC)) {
return "", false
}
return msg, true
}
type Passkey struct {
ID string `xml:",attr"`
Key string `xml:",attr"`
}
func LoadPasskeys(passkeys []Passkey) (map[string][]byte, error) {
names := make(map[string]bool)
out := make(map[string][]byte)
namesByID := make(map[string]string)
for _, passkey := range passkeys {
if names[passkey.ID] {
return nil, fmt.Errorf("duplicate name %q", passkey.ID)
}
names[passkey.ID] = true
keyBytes, err := base64.RawURLEncoding.DecodeString(strings.Map(func(r rune) rune {
if unicode.IsSpace(r) {
return -1
}
return r
}, passkey.Key))
if err != nil {
return nil, fmt.Errorf("invalid key for passkey %q: %s", passkey.ID, err)
}
if len(keyBytes) < 16 {
return nil, fmt.Errorf("invalid key for passkey %q: bad user ID: too short", passkey.ID)
}
id, key := keyBytes[:16], keyBytes[16:]
if _, err := sigVerifier(key); err != nil {
return nil, fmt.Errorf("invalid key for passkey %q: %s", passkey.ID, err)
}
if _, ok := out[string(id)]; ok {
return nil, fmt.Errorf("passkeys %q and %q have duplicate ID %d", namesByID[string(id)], passkey.ID, id)
}
out[string(id)] = key
namesByID[string(id)] = passkey.ID
}
return out, nil
}
func sigVerifier(keyBytes []byte) (func(msg, sig []byte) bool, error) {
key, err := x509.ParsePKIXPublicKey(keyBytes)
if err != nil {
return nil, err
}
switch key := key.(type) {
case *ecdsa.PublicKey:
return func(msg, sig []byte) bool {
hash := sha256.Sum256(msg)
return ecdsa.VerifyASN1(key, hash[:], sig)
}, nil
case *rsa.PublicKey:
return func(msg, sig []byte) bool {
hash := sha256.Sum256(msg)
return rsa.VerifyPKCS1v15(key, crypto.SHA256, hash[:], sig) == nil
}, nil
default:
return nil, fmt.Errorf("unsupported key type")
}
}
func VerifyPubKey(pubKey, msg, sig []byte) error {
verify, err := sigVerifier(pubKey)
if err != nil {
return err
}
if !verify(msg, sig) {
return fmt.Errorf("message failed validation")
}
return nil
}
const challengeExpiry = 10 * time.Minute
var (
challengeMu sync.Mutex
challenges = make(map[string]time.Time)
)
func NewChallenge() ([]byte, bool) {
buf := make([]byte, 32)
rand.Read(buf)
now := time.Now()
challengeMu.Lock()
if len(challenges) >= 100 {
challengeMu.Unlock()
return nil, false
}
challenges[string(buf)] = now
challengeMu.Unlock()
return buf, true
}
func Login(user, authData, clientData, sig []byte, passkeys map[string][]byte, selfURL *url.URL) error {
pubKey, ok := passkeys[string(user)]
if !ok {
return fmt.Errorf("no user with the given ID")
}
clientDataHash := sha256.Sum256(clientData)
if err := VerifyPubKey(pubKey, slices.Concat(authData, clientDataHash[:]), sig); err != nil {
return fmt.Errorf("challenge failed: %s", err)
}
var cd struct {
Type string `json:"type"`
Challenge string `json:"challenge"`
Origin string `json:"origin"`
CrossOrigin bool `json:"crossOrigin"`
}
if err := json.Unmarshal(clientData, &cd); err != nil {
return fmt.Errorf("bad client data: invalid JSON: %s", err)
}
challenge, err := base64.RawURLEncoding.DecodeString(cd.Challenge)
if err != nil {
return fmt.Errorf("bad client data: bad challenge: %s", err)
}
challengeMu.Lock()
initiated, ok := challenges[string(challenge)]
delete(challenges, string(challenge))
challengeMu.Unlock()
if !ok {
return fmt.Errorf("request already consumed")
}
if time.Since(initiated) > challengeExpiry {
return fmt.Errorf("challenge is too old; please try again")
}
if cd.Type != "webauthn.get" || cd.Origin != selfURL.String() || cd.CrossOrigin {
return fmt.Errorf("bad client data")
}
expectedRPHash := sha256.Sum256([]byte(selfURL.Hostname()))
const flagUserPresence, flagUserVerification = 0x01, 0x04
if len(authData) < 37 || !bytes.Equal(authData[:32], expectedRPHash[:]) || authData[32]&(flagUserPresence|flagUserVerification) != (flagUserPresence|flagUserVerification) {
return fmt.Errorf("bad authenticator data")
}
return nil
}
func CleanChallenges() {
log.Printf("Cleaning expired challenges")
now := time.Now()
challengeMu.Lock()
for challenge, initiated := range challenges {
if now.Sub(initiated) > challengeExpiry {
delete(challenges, challenge)
}
}
challengeMu.Unlock()
}
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