Secure AJAX Handler with Nonce Verification

// Register the AJAX action for logged-in users.
add_action( 'wp_ajax_my_custom_action', 'handle_my_custom_action' );

/**
 * Handle the AJAX request securely.
 *
 * @return void
 */
function handle_my_custom_action(): void {
    // Verify the nonce.
    check_ajax_referer( 'my_custom_nonce', 'security' );

    // Sanitize input.
    $item_id = isset( $_POST['item_id'] ) ? absint( $_POST['item_id'] ) : 0;

    if ( ! $item_id ) {
        wp_send_json_error( array( 'message' => __( 'Invalid item.', 'theme-domain' ) ) );
    }

    // Your business logic here.
    $result = get_post( $item_id );

    if ( ! $result ) {
        wp_send_json_error( array( 'message' => __( 'Item not found.', 'theme-domain' ) ) );
    }

    wp_send_json_success( array(
        'title' => esc_html( $result->post_title ),
    ) );
}

// Enqueue and localize the script.
add_action( 'wp_enqueue_scripts', function() {
    wp_enqueue_script( 'my-ajax-script', get_template_directory_uri() . '/assets/js/ajax.js', array( 'jquery' ), '1.0.0', true );
    wp_localize_script( 'my-ajax-script', 'myAjax', array(
        'url'   => admin_url( 'admin-ajax.php' ),
        'nonce' => wp_create_nonce( 'my_custom_nonce' ),
    ) );
} );