How to limit anonymous access

I know it sounds like an oxymoron but the reality is that we are trying to publish some of the widgets on our company intranet site. The problem is our Piwik in running in the DMZ so a limited number of users can access the stats while they are traveling.

Is there a way I can limit anonymous access from a specific IP? We are using WordPress as out intranet server. Mybe there is a plugin. I don’t want people finding our Piwik server and viewing the stats.

Thank you,