What are the differences between using session_register and directly setting session variables in PHP, and how does it affect session management in web applications?

Using session_register is deprecated in PHP and can lead to security vulnerabilities as it automatically registers global variables in the session. It is recommended to directly set session variables using the $_SESSION superglobal array to avoid these issues and have better control over session management in web applications.

// Using $_SESSION superglobal to set session variables
$_SESSION['username'] = 'john_doe';
$_SESSION['email'] = 'john.doe@example.com';