user auth patches

[Tor Lillqvist]

 > > The SID is a structure but there exists a functions for serialization,
 > > ConvertSidToStringSid. Therefore a string would be fine, the questions
 > > remains if we should use a wchar_t or char?

The serialization is always ASCII only, so I don't see any gain in
using wide characters.

 > We could also use a copy of the struct if it can be assigned by value 
 > and has a fixed size

It's variable length structure.

--tml