wp-custom-login-form-logo-url.php

<?php

add_action('login_enqueue_scripts', '_pit_login_logo_style');
function _pit_login_logo_style(){ ?>
    <style type="text/css">
        #login h1 a, .login h1 a {
            background-image: url(<?php header_image(); ?>);
            height:80px;
            width:320px;
            background-repeat: no-repeat;
            background-size: contain;
        }
    </style>
<?php }

add_filter('login_headerurl', '_pit_login_logo_url');
function _pit_login_logo_url() {
    return home_url();
}

add_filter('login_headertitle', '_pit_login_logo_title');
function _pit_login_logo_title() {
    return get_bloginfo('name');
}