Which field in password credential provider is dedicated to domain

Hi,
I'm wrapping existing password credential provider and need to know the
username, password and domain. Username and password fields are easy to find
among other fields in the wrapped credential by their GUIDs -
CPFG_LOGON_USERNAME, CPFG_LOGON_PASSWORD. Is there a publicky defined GUID
for Domain too? Or how can I correctly find the field in credential for
Domain?

Thanks,
Tomas