SSL_get_verify_result() can only return one error code while the verification
of a certificate can fail because of many reasons at the same time. Only
the last verification error that occurred during the processing is available
The verification result is part of the established session and is restored
when a session is reused.
If no peer certificate was presented, the returned result code is
X509_V_OK. This is because no verification error occurred, it does however
not indicate success. SSL_get_verify_result() is only useful in connection