Please don’t hard-code assumptions

At the NFS layer, yes, at the RPC layer, no. NFSv4 can use strings when getting and setting attributes like file owners or groups or ACLs. At the RPC layer (which is what identifies who is performing a given operation) it still uses numeric IDs, unless you're using kerberos. The NFSv4 design pretty much assumed everyone would want kerberos.

You may already know that, and it's a bit of a digression, apologies. But it causes frequent confusion.