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guard 'copy checkin' behind auth and 'not checked in' check
Unauthenticated users have no way of performing a checkin. If a user is already checked in, they have to check out first. For the latter case, it might be a good idea to still allow a new checkin if the current checkin has already arrived at its destination (and perform an automatic checkout in that case). But that's a different issue that can be addressed later.