Block access to files by IP using X-Forwarded-For

What is the purpose of blocking by X-Forwarded-For IP, instead of the REMOTE_ADDR?

Sometimes a site may be behind a reverse proxy and it may not be possible to add a rule to block a file by IP at the reverse proxy level.  If the reverse proxy is passing the remote client IP in a header like X-Forwarded-For, you can still block by client IP.

Match the header to an IP address and assign it to an environment variable in Apache.  Here is an example of a complete configuration to block remote access to a wordpress login page, except for a certain range of IPs:

<files wp-login.php>
order deny,allow
deny from all
SetEnvIf X-Forwarded-For "192\.168\..*" LocalAccess
SetEnvIf X-Forwarded-For "10\..*" LocalAccess
Allow from env=LocalAccess
</files>

If the IP contained in the X-Forwarded-For header matches one of the regular expressions, it will populate the "LocalAccess" environment variable.

Granular permissions through sudoers

A quick example on how to provide root permissions on specific commands to a specific group of users.

You can create command aliases, which can be very useful when formatting and controlling access to these.

For example:

Cmnd_Alias vi    = /usr/bin/vim

This will match both /usr/bin/vim or just plain vim.

Assigning ROOT permissions to run this command alias to a specific user:

username ALL=(root) vi

And the same for a group:

%groupname ALL=(root) vi

In my example below, I provide access to use all the NGINX service commands on a redhat 6 system, to a new group called nginxadm.

Open up the sudoers file using visudo.

## NGINX USERS - should be part of nginxadm group
# Usage: nginx {start|stop|restart|condrestart|try-restart|force-reload|upgrade|reload|status|help|configtest}
Cmnd_Alias NG           = /sbin/service nginx
Cmnd_Alias NGRES        = /sbin/service nginx restart
Cmnd_Alias NGSTA        = /sbin/service nginx start
Cmnd_Alias NGSTO        = /sbin/service nginx stop
Cmnd_Alias NGSTS        = /sbin/service nginx status
Cmnd_Alias NGCDR        = /sbin/service nginx condrestart
Cmnd_Alias NGTRS        = /sbin/service nginx try-restart
Cmnd_Alias NGFRL        = /sbin/service nginx force-reload
Cmnd_Alias NGUPG        = /sbin/service nginx upgrade
Cmnd_Alias NGRLD        = /sbin/service nginx reload
Cmnd_Alias NGHLP        = /sbin/service nginx help
Cmnd_Alias NGCFG        = /sbin/service nginx configtest
%nginxadm ALL=(root)    NG,NGRES,NGSTA,NGSTO,NGSTS,NGCDR,NGTRS,NGFRL,NGUPG,NGRLD,NGHLP,NGCFG

Thanks to FACLs in Linux, we can also give granular permissions to the NGINX configuration files.