Attachment download issues

Non-public attachments to Docs are served through PHP rather than directly by the webserver. This allows BuddyPress Docs to control access to these Docs. However, users have reported that PHP-served documents can throw "insecure" browser warnings. See eg https://wordpress.org/support/topic/mixed-content-error-when-downloading-attachments/.

In some cases, this problem may be caused by the use of nginx, either as the webserver software itself or as a reverse proxy. If this is the case, ensure that nginx has been configured to redirect private attachment requests, as per the nginx section of the 'Attachment Privacy' wiki page.