Sanity limit for length of user/group names?

Hi,

The NFSv4 RFCs do not specify an upper limit for the length
of a user or group (called Owner/Owner_group in NFSv4) string.

However, PR#260546 notes that a sanity upper limit for their
length is needed.

Is there any constant in FreeBSD that defines the upper limit for
the length of a user or group name?
(I can find the maximum length of a hostname and I think that can
 be used as a safe upper limit for a domain name, as well. The Owner/
 Owner_group names include "@domain" on them.)

Thanks for any help with this, rick