Password protect accounts

[ICTKA]

I recently found Gmail Desktop and use it in our company's warehouse.
We have 2 general Workspace accounts (Gmail for business) our warehouse staff uses to get e.g. packinglist and communicate with our suppliers.
However we have also 3rd party people (mostly customers) walking in the warehouse and they sometime use our computers to lookup things.

I would really like some kind of way to protect the account in Gmail Desktop, so everytime first time one goes to an e-mailaccount, the user is prompted with a (for us simple) password.
Also prompting for the same password if the app has been xx minutes not used would be nice.