Автоматическая авторизация rsync
Можно.


Some  modules  on the remote daemon may require authentication. If so, you will receive a password prompt when you connect. You can avoid the password prompt by setting the environment variable RSYNC_PASSWORD to the password you want to use or using the --password-file option. This may be useful when scripting rsync.

       WARNING: On some systems environment variables are visible to all users. On those systems using --password-file is recommended.

Не в курсе, как оно по возможнностям на NAS. rsync можно настроить как демон, авторизация будет не через SSH. Свой порт, протокол у rsyncd.