How to properly link the Facebook login URL to this PHP block

Question

How can I properly link the Facebook login URL to this PHP block?

add_filter( 'comment_form_defaults', function( $fields ) {
    $fields['must_log_in'] = sprintf( 
        __( '<p class="must-log-in">
             You must <a href="%s">Register</a> or 
             <a href="%s">Login</a> to post a comment.</p>
                or login Via Facebook
             <a href="http://localhost/jedcore/wp-login.php?loginFacebook=1&redirect=http://localhost/jedcore" onclick="window.location = 'http://localhost/jedcore/wp-login.php?loginFacebook=1&redirect='+window.location.href; return false;"> <img src="HereComeTheImage" /> </a>
             ' 
        ),
        wp_registration_url(),
        wp_login_url( apply_filters( 'the_permalink', get_permalink() ) )   
    );
    return $fields;
});