How can I tell how many users are loggin in via apache authentication?

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http://serverfault.com – I have a web site that has some content protected via apache basic authentication. Is there a way for me to tell (from the access logs perhaps?) how many users are actually using the login? Intranet traffic is excluded from having to log in, so I can't just look at how many people are accessing those pages. Thanks. (HowTos)