This code checks if the 'logged_in' session variable is set to true. If it is not set or is set to false, the user is redirected to the login page. Otherwise, the code continues with the web application logic assuming the user is authenticated. The checkAuth function is not part of a package library, but rather is a custom function that can be implemented within a PHP application. It is often used in combination with authentication libraries or frameworks, such as Laravel or Symfony, to simplify the process of checking if a user is authenticated.