Why is the page always displayed in the sub-section?_html/css_WEB-ITnose

I am working on a backend management system that uses cookies to check whether users are logged in to prevent others from knowing the file path and skipping the login page directly. But after entering the path, the login page will jump to the sub-section of my backend, that is, enter the main page of the backend
I would like to ask if there is a solution?

Reply to the discussion (solution)

This should be a problem with the login processing in your background? You must have located the wrong page in the background

Sorry, there may be a problem with the above understanding of your question. If you want to implement that you must log in before you can access the page, you should use cookie identification after successful login, and check the cookie in the page onload event when the user requests the content page

That is, on the first load of each content page When each content page is loaded for the first time, onload is processed in the background and the cookie information is used to determine whether the user is logged in. If not logged in, it will be redirected to the login page

Determine whether the user is logged in. If not, redirect to the login page
if(!$_COOKIE["isLogin"]){
header('<script>window.open("./index.php ","_parent")</script>');
}
But it still doesn't work

About this problem: After entering the path, the login page will jump to the sub-display in my background. Let’s take a screenshot of the flow chart to see