hey all, I managed to get some time and work on this awstats auth problem.
there's 2 settings in the conf file which you can set to check the authentication.
I changed it in a way so eahc sites config has it's own custom settings and it includes the main template config.
the site's config contains the AllowAccessFromWebToFollowingAuthenticatedUsers="m yuser1 myuser2"
Now, attempting to browse someone elses stats with your login now failed with
Error: User 'web15_djtremors' is not allowed to access statistics of this domain/config.
works like a treat.