feat(backend): bcrypt+jwt auth package and admin seeding

backend/internal/auth/auth.go

@@ -0,0 +1,54 @@
+package auth
+
+import (
+	"crypto/subtle"
+	"errors"
+	"time"
+
+	"github.com/golang-jwt/jwt/v5"
+	"golang.org/x/crypto/bcrypt"
+)
+
+var ErrToken = errors.New("invalid token")
+
+func HashPassword(plain string) (string, error) {
+	b, err := bcrypt.GenerateFromPassword([]byte(plain), 12)
+	return string(b), err
+}
+
+func CheckPassword(hash, plain string) bool {
+	return bcrypt.CompareHashAndPassword([]byte(hash), []byte(plain)) == nil
+}
+
+type Claims struct {
+	UID  int64  `json:"uid"`
+	Role string `json:"role"`
+	jwt.RegisteredClaims
+}
+
+func Sign(secret []byte, uid int64, role string) (string, error) {
+	return SignWithTTL(secret, uid, role, 72*time.Hour)
+}
+
+func SignWithTTL(secret []byte, uid int64, role string, ttl time.Duration) (string, error) {
+	t := jwt.NewWithClaims(jwt.SigningMethodHS256, Claims{
+		UID: uid, Role: role,
+		RegisteredClaims: jwt.RegisteredClaims{ExpiresAt: jwt.NewNumericDate(time.Now().Add(ttl))},
+	})
+	return t.SignedString(secret)
+}
+
+func Parse(secret []byte, token string) (*Claims, error) {
+	c := &Claims{}
+	parsed, err := jwt.ParseWithClaims(token, c, func(t *jwt.Token) (any, error) {
+		m, ok := t.Method.(*jwt.SigningMethodHMAC)
+		if !ok || subtle.ConstantTimeCompare([]byte(m.Alg()), []byte("HS256")) != 1 {
+			return nil, ErrToken
+		}
+		return secret, nil
+	}, jwt.WithValidMethods([]string{"HS256"}))
+	if err != nil || !parsed.Valid {
+		return nil, ErrToken
+	}
+	return c, nil
+}