depending on how complicated your set up is, you could possible get away with just defining users in your share definition.
valid users = user1 user2 user3
this also works in reverse
invalid users = user1 user2 user3
there the user1 user2 user3 are individual samba account users.
more info here:
https://www.samba.org/samba/docs/using_samba/ch09.html