Changes the expiration of the WordPress authentication cookie to 365 days if the user ticks the “Remember Me” checkbox.

auth.php

<?php
/**
 * Authentication customizations.
 *
 * @package BJ\Auth
 */

/**
 * Filters the duration of the authentication cookie expiration period.
 *
 * @param int  $length   Duration of the expiration period in seconds.
 * @param int  $user_id  User ID.
 * @param bool $remember Whether to remember the user login. Default false.
 * @return int Duration of the expiration period in seconds.
 */
function bj_set_auth_cookie_expiration( $length, $user_id, $remember ) {
	if ( $remember ) {
		$length = max( $length, 365 * DAY_IN_SECONDS );
	}
	return $length;
}
add_filter( 'auth_cookie_expiration', 'bj_set_auth_cookie_expiration', 10, 3 );