[xmlsec] How to extract x509 certificate

[Aleksey Sanin]

xmlSecNodeX509Certificate is note a certificate but some
references to it. If you want to get these references then
the simples way is to use XPath on the XML tree in memory.

The certificate object itself is crypto library depended.
You can get it by querying corresponding xmlKeyData object
and then getting the crypto api specific structure from it.

Aleksey