How can a PHP developer ensure that only one user can log in without using a MySQL database?

To ensure that only one user can log in without using a MySQL database, a PHP developer can store a unique identifier (such as a session ID or token) in a file or in memory when a user logs in. This identifier can be checked upon subsequent login attempts to determine if a user is already logged in. If the identifier is found, the user can be prevented from logging in again. 

<?php

session_start();

// Check if a unique identifier exists in the session
if(isset($_SESSION['logged_in_user'])) {
    echo "User is already logged in.";
} else {
    // Set a unique identifier for the logged in user
    $_SESSION['logged_in_user'] = true;
    echo "User has successfully logged in.";
}

?>

Keywords

PHP session management cookies authentication security

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