Manually implement c string function with security enhancements - c++

Question

I'm trying to write a replacement for the _tcstok_s function that doesn't skip initial delimiters. (_tcstok_s is a variant of the strtok function that uses TCHARs and includes security enhancements documented at https://msdn.microsoft.com/en-us/library/8ef0s5kh.aspx). I'm doing this due to the annoying behavior of strtok that skips consecutive delimiters. I got the idea from
c++ strtok skips second token or consecutive delimiter.
The thing I don't understand is how to implement the security enhancements that make _tcstok_s better than _tcstok. How to I make sure my re-implementation is as secure as _tcstok_s?
Although my code is C++, I am using C-style strings because I am implementing an MSI DLL.
This is what I have so far, but I don't know how to add the _s security enhancements.
TCHAR *GetNextToken(TCHAR *strToken, const TCHAR *szDelimit, TCHAR **pszContext)
{
if (strToken == NULL)
{
if ((pszContext == NULL) || (*pszContext == NULL))
return NULL;
TCHAR *pToken = _tcspbrk(*pszContext, szDelimit);
TCHAR *szResult = *pszContext;
if (!pToken)
{
*pszContext = NULL;
}
else
{
*pToken++ = _T('\0');
*pszContext = pToken;
}
return szResult;
}
else
{
TCHAR *pToken = _tcspbrk(strToken, szDelimit);
if (!pToken)
{
*pszContext = NULL;
}
else
{
*pToken++ = _T('\0');
*pszContext = pToken;
}
return strToken;
}
}