Force Login for a WordPress Attachment

<p>Pass in the query-param "file" that is a numeric value of the attachment ID in WordPress<br />
Example: http://www.mysite.com/loader/?file=12804</p>

<?php
//  load file pass-through
//  include the WP environment
    include_once( $_SERVER['DOCUMENT_ROOT'] . '/wp-load.php' );

//  IF USER IS NOT LOGGED IN, FORCE THE LOGIN
if( !is_user_logged_in() ):

    get_header(); ?>
    <section id="content">
        <div class="layout">

            <aside id="sidebar">
                <?php get_sidebar(); ?>
            </aside>

            <article id="main">
                <h1>Login Required to View this Resource</h1>
                <?php wp_login_form(); ?>
            </article>

        </div>
    </section>
    <?php
    get_footer();

else:
//  set the incoming FILE ID to a var, and then look up the file
//  if the param is NOT SET or is NOT A NUMBER then display an error
    $fileID = ( !is_numeric( $_GET['file'] ) || !isset( $_GET['file'] ) ? null : $_GET['file'] );

//  get the file object
    $fileObj = get_post( $fileID );

//  display error if ID ENDS UP BEING NULL
    if( is_null( $fileObj ) ):

        echo 'There was an error loading the file.  Please check the URL and try again.  If this error persists, please contact the website administrator with the TITLE and URL of this file.  Thank you!';

    else:

        $file = array();
        $file['location']   = $_SERVER['DOCUMENT_ROOT'] . str_replace( site_url(), '', $fileObj->guid );
        $file['url_parts']  = explode( '/', $file['location'] );
        $file['save_as']    = end( $file['url_parts'] );
        $file['mimetype']   = $fileObj->post_mime_type;

        header("Content-Type: application/octet-stream");
        header("Content-Transfer-Encoding: Binary");
        header("Content-disposition: attachment; filename=\"".$file['save_as']."\"");
        echo readfile( $file['location'] );

    endif;

endif;
?>