Hi,
NFS server exports (opens) the directory/filesystem to your NFS client. It does not handle users by user names. The users are handled by UID (User ID) and GID (Group ID) defined in the UNIX. If you simulate the same UID and GID from the client as the UNIX permissions are set, then you are ready with the permissions. But it may have security issues ...
Example:
nfsserver:
mkuser id=777 test
chmod 700 /nfsserverdir
mknfsexp -d /nfsserverdir -t rw -c nfsclient -B
nfsclient:
mkuser id=777 test
mknfsmnt -f /nfsdir -d /nfsserverdir -h nfsserver -n -N -a -t rw -w bg -Y -Z -X -H -j -q -s
(or just mount nfsserver:/nfsserverdir /nfsdir) - I prefer the mknfsmnt.
There was a subsystem called pcnfsd invoked from the inetd, that forced the NFS client to authenticate itself, but if the authentication (username+password) was successful, it let the NFS client to connect the NFS filesystem as a usual NFS mount.
So, the security is better, but it is the case again - if you want to dig more into NFS security ...