On unix systems, when creating the default authentication token
use getgid() as the group instead of -1.
Recent linux knfsd do not allow grp==-1

On windows there are no uid/gids in the traditional sense so there I still specify a default credential of uid==gid==-1 :
	rpc->auth = authunix_create("LibNFS", 65535, 65535, 0, NULL);

This is I think the sanest/safest thing to do since most servers will have
special handing of -1 meaning 'nobody' or similar.
This should work on many/most servers and give the user the minimum available
access allowed for 'nobody'.

I think on windows (or AROS for that matter) applications will probably have
to invoke and set the credentials themself explicitely.
Those apps probably, unfortunately, also need to have a configuration
setting to select which uid/gid to use when talking to the server.
(or they could hardcode it)

rpc_set_auth(rpc, libnfs_authunix_create("hostname", uid, gid, 0, NULL))
should do the trick if they call immediately after creating the rpc/nfs context.

But dont set it to 0,0 root/root for uid/gid.
First of all, most servers have root-squash so they will re-map this uid/gid
to 'nobody' internally.
But, if the user uses a server that does not do root-squash, then setting this to 0,0 would mean that your app now access the nfs share as root   which is probably not what you want.