title: Firebase app - keep track of the time of user's last access?
body: <p>I noticed Firebase stores user creation time and user login time ny default, but not the time the user last accessed the app. Would I need to store this info separately?
  I notice some of my users show as having logged in weeks ago, yet I have been using the app everyday. Keeping track of when the user last accessed the app is useful for admin purposes.</p>