How to verified user autentication via Sid

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C++

C

COM

We have a client server architecture, both client and server are on windows XP system the server is in the domain, the client send to the server this authentications data:
UserName
DomainName
Sid

In the client side these data are obtained using:

// Retrieve the user information from the token.
if (!GetTokenInformation(hToken, TokenUser, ptiUser, cbti, &cbti))
   __leave;
// Retrieve user name and domain name based on user's SID.
if (!LookupAccountSid(NULL, ptiUser->User.Sid, szUser, pcchUser,
      szDomain, pcchDomain, &snu))
   __leave;

Now on the server I need to verified if this user is logged into domain, we thought to use the LDAP API on the server, how can I do this?
The sid from client is the same as the user in the domain controller?