Displays the registered WordPress Site Icon as a logo on the Login Form

wp-site-icon-login.php

<?php
/**
 * Displays the registered Site Icon as a logo on the Login Form
 */
function fltnt_add_site_icon_to_login() {

    if ( function_exists( 'has_site_icon' ) && has_site_icon() ) {
        ?>
        <style type="text/css">
            .login h1 a {
                background-image: url(<?php site_icon_url(); ?>);
            }
        </style>
        <?php
    }
}

add_action( 'login_enqueue_scripts', 'fltnt_add_site_icon_to_login' );