What are the security considerations to keep in mind when implementing admin-only functions in PHP scripts?

When implementing admin-only functions in PHP scripts, it is crucial to ensure that unauthorized users cannot access or execute these functions. This can be achieved by implementing user authentication and authorization checks to verify that the user accessing the admin functions is indeed an admin. Additionally, it is important to sanitize and validate user input to prevent any security vulnerabilities such as SQL injection or cross-site scripting attacks.

// Check if user is authenticated and is an admin before executing admin-only functions
session_start();

if(isset($_SESSION['user']) && $_SESSION['user']['role'] == 'admin') {
    // Admin-only functions here
    // Example: delete_user($user_id);
} else {
    // Redirect unauthorized users to login page or display an error message
    header("Location: login.php");
    exit();
}