[Samba] Override unjoined computername with SAMDOM to allow connection to share

[Alex]

Hi,

I have a Samba 4 domain (separate DC and file server), with a bunch of
Win/Mac/Lin domain joined machines, everything works on that side.

I have a machine with a read-only SOC which can't take a \ or @ in the
username, and in the samba file server logs, I see it is authenticating
with it's computername in place of the domain:

[2023/08/02 09:46:24.265533,  3]
../source3/auth/auth.c:189(auth_check_ntlm_password)
  check_ntlm_password:  Checking password for unmapped user
[]\[USERNAME]@[computername] with the new password interface
[2023/08/02 09:46:24.265596,  3]
../source3/auth/auth.c:192(auth_check_ntlm_password)
  check_ntlm_password:  mapped user is: []\[USERNAME]@[computername]
[2023/08/02 09:46:24.269665,  3]
../source3/auth/check_samsec.c:399(check_sam_security)
  check_sam_security: Couldn't find user 'USERNAME' in passdb.
[2023/08/02 09:46:24.269763,  2]
../source3/auth/auth.c:332(auth_check_ntlm_password)
  check_ntlm_password:  Authentication for user [USERNAME] -> [USERNAME]
FAILED with error NT_STATUS_NO_SUCH_USER, authoritative=1


Is there a way I can map the USERNAME at computername to USERNAME at SAMDOM, such
as with a username map file or other mechanism?

Other unjoined devices can map the same share without issues, but they
allow me to authenticate as SAMDOM\username or username at samdom.tld.

Thanks,

Peter