Customize WordPress Default Login URL Returned by wp_login_url() For adding custom login template via WordPress page template feature.

wp_custom_login_url.php

<?php
if(!function_exists('sekaiju_login_page')):
/**
 * Change Default Login Url Regurned by wp_login_url()
 * @param string $login_url
 * @param string $redirect
 * @return string
 */
add_filter( 'login_url', 'custom_login_url', 10, 2 );
function custom_login_url( $login_url, $redirect ) {
    $postID = YOUR-CUSTOM-LOGIN-PAGE-ID;//get_option('custom_login');
	$redirect_to = '';
	if($redirect != "")
		$redirect_to = '?redirect_to='.$redirect;
	return get_permalink($postID) . $redirect_to;
}
endif;