How can the transition from PHP 4 to PHP 7 impact session handling and login functionality in a web application?

Transitioning from PHP 4 to PHP 7 can impact session handling and login functionality in a web application because PHP 7 introduced changes in how sessions are managed and how passwords are hashed. To address this, it is important to update session handling code to comply with the new session functions in PHP 7 and to use stronger password hashing algorithms like bcrypt for improved security.

// Update session_start() function to use the $_SESSION superglobal
session_start();

// Update password hashing to use bcrypt
$options = [
    'cost' => 12,
];
$hashed_password = password_hash($password, PASSWORD_BCRYPT, $options);