Sonos is primarily designed for use in the home where this is typically not an issue, not in a office.  They do however have a pro - business model that does have the sort of access security you’re looking for, but it comes with a significant subscription fee.  It’s not really designed for single users in an office either.

I would talk to your IT to see if you can get your own private wifi network setup.  This can be done with a cheap travel router.  You could also disconnect the Era 300 from wifi and use it as bluetooth speaker, but that would significantly reduce the functionality of the speaker.

Thank you but this seems to overlook a very simple way to address a privacy issue that exists regardless of where the network is, and would then make their equipment use more versatile. Add user permission options and it’s fixed. @Sonos 

User permissions are one of the most complicated and maintenance heavy tasks in all of software engineering.  And for every “just don’t allow them access” requests, you will get a dozen “let them do this but not that” requests.  So for an implementation which would satisfy enough users to justify itself, not only would it take up a huge amount of development hours, the customer support needed would be astronomical.