Why we want to enhance this feature?

There's no accurate measure on the number of active users on a concourse cluster.

We proposed two ways of doing this:

1. Parsing Log. As @pivotal-jwinters suggested, we could filter out the event atc.dex.event
   from the log for the past 60 days.
2. New DB Table. @YoussB proposed to add a new database table active_user in current DB to update the user last_login_date to enumerate the active users. This would require additional changes to the current login flow. The table schema may look like below:

And the Pros and Cons we (@pivotal-bin-ju and I) can think about for now:

Issue Status

Working is being done on the feature/4035-active-users branch

Sidenote (@taylorsilva): when logging in as a user that's not part of any team (guest user in docker-compose) we get a HTTP 400 back and a blank screen at the /sky/callback endpoint. Logs show "error":"user doesn't belong to any team". Thinking this may be a regression. This note is to remind us to check this out and potentially report.
and fly:

fly -t local login -u guest -p guest
logging in to team 'main'

error: oauth2: cannot fetch token: 400 Bad Request
Response:

Sidenote 2 (@cirocosta): Concourse allows operators to set the duration of the tokens that are generated (see