You can use "user/password" database setup w/ SAMBA but I prefer to use IP address's. You can specify entire networks by doing something like 192.168. or specify all the way down to a static IP.
This allows the local device *loopback/127.0.0.1* and the ENTIRE 192.168.*.* network and 10.*.*.* network. (And Deny everything else)
This shares the ROOT of the Filesystem. Not Advisable!
Note: I have had issues sharing a directory high up the file tree due to permissions. I now use BIND to BIND a top shared directory to /srv/smb.
Read more on Binding with FSTAB