certificates: Retrieve serial numbers in canonical form

The x509 plugin retrieves serial numbers with two's complement
encoding whereas the openssl plugin partially returns them without
leading zeroes.

Serial numbers in X.509 certificates, X.509 CRL, X.509 attribute
certificates, OCSP Requests and OCSP responses are now returned in
canonical form without prepended zero octets.

src/libstrongswan/plugins/x509/x509_ocsp_response.c

@@ -1,7 +1,7 @@
 /*
  * Copyright (C) 2017-2019 Tobias Brunner
  * Copyright (C) 2008-2009 Martin Willi
- * Copyright (C) 2007-2015 Andreas Steffen
+ * Copyright (C) 2007-2022 Andreas Steffen
  * Copyright (C) 2003 Christoph Gysin, Simon Zwahlen
  *
  * Copyright (C) secunet Security Networks AG
@@ -370,7 +370,7 @@ static bool parse_singleResponse(private_x509_ocsp_response_t *this,
 				response->issuerKeyHash = object;
 				break;
 			case SINGLE_RESPONSE_SERIAL_NUMBER:
-				response->serialNumber = object;
+				response->serialNumber = chunk_skip_zero(object);
 				break;
 			case SINGLE_RESPONSE_CERT_STATUS_GOOD:
 				response->status = VALIDATION_GOOD;