I have some code, with which I'm trying to get the current session user token:

#include <Wtsapi32.h>

DWORD activeSessionId = WTSGetActiveConsoleSessionId();

HANDLE currentToken;
BOOL queryRet = WTSQueryUserToken(activeSessionId, &currentToken);

if (!queryRet) {
    DWORD err = GetLastError();
    return 0;
}

Value of err is 1314.

Update 1

No luck so far, tried to grant the current process SE_TCB_NAME - but still get same error from WTSQueryUserToken (1314).

HANDLE process = GetCurrentProcess();

HANDLE processToken;
BOOL openTokenRet = OpenProcessToken(
    process, TOKEN_ADJUST_PRIVILEGES | TOKEN_QUERY, &processToken);

if (!openTokenRet)
{
    DWORD err = GetLastError();
    return 0;
}

TOKEN_PRIVILEGES tokenPrivs;
BOOL lookupRet = LookupPrivilegeValue(
    NULL, SE_TCB_NAME, &tokenPrivs.Privileges[0].Luid);

if (!lookupRet)
{
    DWORD err = GetLastError();
    return 0;
}

tokenPrivs.PrivilegeCount = 1;
tokenPrivs.Privileges[0].Attributes = SE_PRIVILEGE_ENABLED;

BOOL adjustRet = AdjustTokenPrivileges(
    processToken, FALSE, &tokenPrivs, 0, (PTOKEN_PRIVILEGES)NULL, 0);

if (!adjustRet)
{
    DWORD err = GetLastError();
    return 0;
}

// get the user in the active session
HANDLE currentToken;
BOOL queryRet = WTSQueryUserToken(activeSessionId, &currentToken);

if (!queryRet) {
    DWORD err = GetLastError();
    return 0;
}

Update 2:

Added some more debug info, but prevState.PrivilegeCount is 0...

TOKEN_PRIVILEGES prevState;
DWORD prevStateLen = 0;

BOOL adjustRet = AdjustTokenPrivileges(
    processToken, FALSE, &tokenPrivs, 
    sizeof(TOKEN_PRIVILEGES), &prevState, &prevStateLen);

DWORD adjustErr = GetLastError();
if (!adjustRet)
{
    return 0;
}

Solution:

Looks like WTSQueryUserToken can only be used when running as LocalSystem, which means I'll have to run as a service and debug from there... Doh!

Error 1314 is ERROR_PRIVILEGE_NOT_HELD. You need SE_TCB_NAME privilege to call WTSQueryUserToken.

This privilege is typically held only by code running as Local System. If this privilege is present in your token, but disabled, you can use AdjustTokenPrivileges to enable it. Since SE_TCB_NAME is a potentially very dangerous privilege to have, you should disable it again immediately after you use it. An easy way to see if you have this privilege is with Process Explorer in the Security table of the process properties window.

Per Update 1 - is AdjustTokenPrivileges return success, but GetLastError() is set to ERROR_NOT_ALL_ASSIGNED? MSDN indicates it could return this if privileges weren't enabled. Can you verify that your process does have SE_TCB_NAME privilege, but it is disabled? What account is your process running as?