Perhaps I'm just thinking too hard about this...
But when I create a share, I can choose to either restrict access by users/groups or to anyone who tries to access the share.
But, what if I want to let anyone read without needing to authenticate, but allow only certain created users to read and also write to the share?
For example, on my local network I would like to allow anyone to simply browse to the NAS and access the share to read documents. Then, on my machine I would simply map the share with my create user name and password, allowing only me to write to it.