Implement JWT authentication and app passkey support

- Add JWT token generation and validation
- Implement bcrypt password hashing
- Create auth service with register/login/refresh/logout
- Add app passkey generation and management
- Implement protected routes and auth middleware
- Add comprehensive tests for new functionality

internal/auth/jwt.go

@@ -0,0 +1,61 @@
+package auth
+
+import (
+	"fmt"
+	"time"
+
+	"github.com/golang-jwt/jwt/v5"
+	"github.com/google/uuid"
+)
+
+// Claims represents the JWT claims for MyGO access tokens.
+type Claims struct {
+	jwt.RegisteredClaims
+	UserID string `json:"uid"`
+}
+
+// GenerateAccessToken creates a signed JWT access token for a user.
+func GenerateAccessToken(userID string, secret []byte, ttl time.Duration) (string, error) {
+	now := time.Now()
+	claims := Claims{
+		RegisteredClaims: jwt.RegisteredClaims{
+			ID:        uuid.NewString(),
+			IssuedAt:  jwt.NewNumericDate(now),
+			ExpiresAt: jwt.NewNumericDate(now.Add(ttl)),
+		},
+		UserID: userID,
+	}
+
+	token := jwt.NewWithClaims(jwt.SigningMethodHS256, claims)
+	signed, err := token.SignedString(secret)
+	if err != nil {
+		return "", fmt.Errorf("sign token: %w", err)
+	}
+
+	return signed, nil
+}
+
+// GenerateRefreshToken creates a signed JWT refresh token.
+func GenerateRefreshToken(userID string, secret []byte, ttl time.Duration) (string, error) {
+	return GenerateAccessToken(userID, secret, ttl)
+}
+
+// ParseToken validates and parses a JWT token string.
+func ParseToken(tokenString string, secret []byte) (*Claims, error) {
+	token, err := jwt.ParseWithClaims(tokenString, &Claims{}, func(t *jwt.Token) (any, error) {
+		if _, ok := t.Method.(*jwt.SigningMethodHMAC); !ok {
+			return nil, fmt.Errorf("unexpected signing method: %v", t.Header["alg"])
+		}
+		return secret, nil
+	})
+	if err != nil {
+		return nil, fmt.Errorf("parse token: %w", err)
+	}
+
+	claims, ok := token.Claims.(*Claims)
+	if !ok || !token.Valid {
+		return nil, fmt.Errorf("invalid token claims")
+	}
+
+	return claims, nil
+}