We can pre-populate the app with your attendee list so only your attendees gain access.  The second option would be to provide your attendees a single event code (password) and after joining the event your attendees will be required to enter the valid event code.   To add additional layers of security, we can also control which features/modules are available to attendees based on attendee groups.  We can also enable the option to hide your app from the search results within the app container so only users on your attendee list can find and access the app.