add authentication method

internal/auth/jwt.go

@@ -0,0 +1,64 @@
+package auth
+
+import (
+	"errors"
+	"time"
+
+	"github.com/golang-jwt/jwt/v5"
+)
+
+var (
+	ErrInvalidToken = errors.New("invalid token")
+	ErrExpiredToken = errors.New("token expired")
+)
+
+// Claims represents JWT claims
+type Claims struct {
+	UserID string `json:"user_id"`
+	Role   string `json:"role"`
+	jwt.RegisteredClaims
+}
+
+// GenerateToken generates a JWT token for a user
+func (s *Service) GenerateToken(userID, role string) (string, error) {
+	expirationTime := time.Now().Add(24 * time.Hour) // Token valid for 24 hours
+
+	claims := &Claims{
+		UserID: userID,
+		Role:   role,
+		RegisteredClaims: jwt.RegisteredClaims{
+			ExpiresAt: jwt.NewNumericDate(expirationTime),
+			IssuedAt:  jwt.NewNumericDate(time.Now()),
+			NotBefore: jwt.NewNumericDate(time.Now()),
+		},
+	}
+
+	token := jwt.NewWithClaims(jwt.SigningMethodHS256, claims)
+	return token.SignedString(s.jwtSecret)
+}
+
+// ValidateToken validates a JWT token and returns the claims
+func (s *Service) ValidateToken(tokenString string) (*Claims, error) {
+	token, err := jwt.ParseWithClaims(tokenString, &Claims{}, func(token *jwt.Token) (interface{}, error) {
+		if _, ok := token.Method.(*jwt.SigningMethodHMAC); !ok {
+			return nil, errors.New("unexpected signing method")
+		}
+		return s.jwtSecret, nil
+	})
+
+	if err != nil {
+		// Check if token is expired
+		if errors.Is(err, jwt.ErrTokenExpired) {
+			return nil, ErrExpiredToken
+		}
+		// All other errors are invalid tokens
+		return nil, ErrInvalidToken
+	}
+
+	claims, ok := token.Claims.(*Claims)
+	if !ok || !token.Valid {
+		return nil, ErrInvalidToken
+	}
+
+	return claims, nil
+}