Error 403 is an webserver level error, just make sense to search in webserver logs.
Might be you looking at the wrong logs.
It may be that a wrong configuration can send requests to other areas, thus logging into different file logs.
If in apache virtual hosts are not being logged events, the first bet is to search in main server error log, at '/usr/local/apache/logs/error_log'.
As you are mentioning to use nginx, you must to check if the events are being logged in nginx logs.
You must check where in your configuration, normally in '/etc/nginx/nginx.conf', and the error log in '/var/log/nginx/error.log'.
Might be too your configuration is not logging events in the severity is wish.
Check the directive "error_log" in the configuration file.
Regards,
Netino