Add User certificate audit.

Description

Ticket #1528 (closed) Has added support of Auditing Events (and entries). However, currently, user certificates which failed validation outside S2OPC explicit scope (typically in the user authentication callback when users try to connect using via X509) are not Audited.

Code version identification

See after merge of #1528 (closed)

Current behavior

No Auditing of user certificates.

Expected behavior

User certificates failure may be audited.

Security impact

Yes: Auditing user certificate may allow cybersecurity analysis to identify unattended connections.

Implementation

So as to ensure that all audits are done without relying on User exported constraints, this implies that the certificate checking itself should be able to realize the Audit.

But this is not currently possible because the Certificate check is done in "Common/crypto" context, which has no knowledge of ClientServer (where Audit are handled). Some context may be set by SOPC_Audit_Initialize.