请问php网站后台密码怎么修改

// 假设用户已通过身份验证 $userId = $_SESSION['user_id'];  // 获取表单数据 $newPassword = $_POST['new_password']; $confirmPassword = $_POST['confirm_password'];  // 验证新密码 if ($newPassword !== $confirmPassword) {     echo "新密码和确认密码不匹配！";     exit; }  // 加载用户信息 $user = getUserById($userId);  // 验证旧密码 if (!password_verify($_POST['old_password'], $user['password_hash'])) {     echo "旧密码错误！";     exit; }  // 更新密码 $newPasswordHash = password_hash($newPassword, PASSWORD_DEFAULT); updateUserPassword($userId, $newPasswordHash);  // 清除会话 session_unset(); session_destroy();  echo "密码修改成功，请重新登录。";