What are the potential security risks associated with using session variables in PHP for user authentication?

Using session variables for user authentication in PHP can pose security risks if not implemented correctly. One potential risk is session hijacking, where an attacker steals the session ID and impersonates the user. To mitigate this risk, it is important to regenerate the session ID after a user logs in or changes their privilege level.

session_start();

// User authentication code here

// Regenerate session ID
session_regenerate_id(true);