Feature Request: Log SSL events

[dcornejo]

For security audit we should log all connections to the HTTP server.

SSL failures should be logged at a higher severity level (maybe Error) so that they can be filtered from successes (Info or Notice?).

[olofhagsand]

Can you please provide examples?
Potential candidates are

1. in read_ssl():;
   clicon_log(LOG_WARNING, "%s SSL_read(): %s", FUNCTION, strerror(errno));
2. in errors from SSL_write in native_buf_write()
   etc.

[olofhagsand]

Added syslog on NOTICE level for failed cert verification.
Example:

Jun  8 13:11:11 Alarik clixon_restconf[17371]: Cert error: /CN=limited/emailAddress=limited@foo.bar/O=Clixon/L=Stockholm/C=SE: certificate has expired