[PD2] Gateway login, logout and auth middleware done.

Co-authored-by: tsousa111 <tiagao2001@hotmail.com>

Projs/PD2/internal/gateway/jwt.go

@@ -0,0 +1,62 @@
+package gateway
+
+import (
+	"errors"
+	"os"
+	"time"
+
+	"github.com/golang-jwt/jwt/v4"
+	"golang.org/x/crypto/bcrypt"
+)
+
+// HashPassword hashes the given password and returns the hashed password as a byte slice.
+func HashPassword(password string) ([]byte, error) {
+	hashedPassword, err := bcrypt.GenerateFromPassword([]byte(password), bcrypt.DefaultCost)
+	if err != nil {
+		return nil, err
+	}
+	return hashedPassword, nil
+}
+
+// CheckPassword compares a bcrypt hashed password with its possible plaintext equivalent.
+func CheckPassword(hashedPassword []byte, password string) error {
+	return bcrypt.CompareHashAndPassword(hashedPassword, []byte(password))
+}
+
+// GenerateJWT generates a JWT token with a specified user ID and expiry time.
+func GenerateJWT(uid string) (string, error) {
+	claims := &jwt.MapClaims{
+		"sub":   uid,
+		"exp": time.Now().Add(time.Hour * 24).Unix(),
+	}
+
+	token := jwt.NewWithClaims(jwt.SigningMethodHS256, claims)
+	tokenString, err := token.SignedString([]byte(os.Getenv("SECRET_KEY")))
+	if err != nil {
+		return "", err
+	}
+	return tokenString, nil
+}
+
+// ValidateJWT validates the given JWT token and returns the user id if valid.
+func ValidateJWT(tokenString string) (string, error) {
+	token, err := jwt.Parse(tokenString, func(token *jwt.Token) (interface{}, error) {
+		return []byte(os.Getenv("SECRET_KEY")), nil
+	})
+
+	if err != nil {
+		return "", err
+	}
+
+	if !token.Valid {
+		return "", errors.New("invalid token")
+	}
+	if claims, ok := token.Claims.(jwt.MapClaims); ok && token.Valid {
+        if  time.Now().Unix() > claims["exp"].(int64) {
+            return "", errors.New("JWT token has expired")
+        }
+        return claims["sub"].(string),nil
+	} else {
+        return "",errors.New("Failed to get jwt claims")
+	}
+}