[xmlsec] Microsoft CAPI support with hardware token

[xs04.jmdesp at free.fr]

Quoting Wouter <wsh at xs4all.nl>:
> [...] Didn't you get problems with the
> default CSP that is selected with the MS CryptoAPI implementation? I can
> remember from earlier tests (not with xmlsec lib) that you explicitly
> had to select a certain provider here, and that is not configurable at
> this moment with xmlsec lib (+ mscrypto).

When running step by step, I saw some not good looking things with regard to
that, but it seems to work at the end.
 
> [...] A
> solution here could be to create some kind of reference count for this
> context [...]. I think it can be done via the
> _xmlSecMSCryptoKeyDataCtx struct. This refcount must be shared between
> the different key contexts.

Yes. Not necessarily that hard. It doesn't look pretty, but I could do it with
rather minor changes. The fact the library is clean and only one file ever
accesses _xmlSecMSCryptoKeyDataCtx does make things a lot easier.

But I still have problems at the end. Might be in my code, didn't investigate fully.

> My only question right now would be: Do we
> need to synchronize access to this context (I think not)?

You mean WRT multi-threaded access ? I didn't do it, but it sounds like it :-)