I'm sharing the dashboard with internal users within my organization using shinyapps private dashboard system. But even if someone doesn't have access to their email because they don't work with our organization anymore, they could still log in to shinyapps.io using the email+password combination. The number of users are high and I cannot keep track of everyone leaving the organization. I want to prevent this by adding some security measures to login process. The simplest one could be sending a code to user's email (the email they used to log into shinyapps.io) and prompt them to enter the code in order to start using the dashboard. Any other suggestion that makes sure the email added to shiny dashboard is still active is welcome as well.