Holds user's authentication domain (if provided).

A String value.  

object.Domain [= value]

The Domain Property syntax has these parts:

Domain contains information user's domain when NTLM challenge-response authentication was performed. It can be empty even when NTLM is used (and surely is empty when other type of authentication is used). You can use it to decide whether user has supplied valid login credentials or not, in UserAuthenticate event.