Are there REST API calls available to determine the number of unique visitors to the crucible instance for a specific time period?
or is there an alternate way to achieve this functionality?
I just created a small plugin for you which will inject Google Analytics into your FishEye/Crucible instance.
The plugin can be downloaded via https://maven.atlassian.com/public/com/atlassian/plugins/fecru-ga/fecru-ga-plugin/1.1/fecru-ga-plugin-1.1.jar and is open source is at http://bitbucket.org/atlassian/fecru-google-analytics/
Once installed, refresh the admin screen and click on the Google Link in the Global Settings.
From here you can configure your Google Analytics tracking ID.
Tarun: I don't see any timestamp that is updated when user logs in, but Crucible does store information about the last repository, user, review, and project that someone visits. Using that data, I was able to write a query to get the total number of unique users between two dates. The query below is written for Oracle, so you'll need to tweak it for the database that you're using.
select count (distinct cru_user_name) as total_active_users from cru_recently_visited where trunc(DATE '1970-01-01' + (cru_last_viewed/1000/86400)) between DATE '2013-09-01' and DATE '2013-10-01';
You could use Google Analytics to get this data. Below are some links that talk about setting up Confluence with Google Analytics.