If a client certificate is requested this flag determines which certificate is used by a zero based numeric index. By default the first is used (0).
Note:
There are no APIs to determine the available certificates through WinInet so the numeric index is unfortunately the only way that you can specify a certificate at this point
o.nClientCertificateIndex
See also:
Class wwHTTP
West Wind Client Tools
wwHTTP::nClientCertificateIndex