crypto: expose signatureAlgorithm on X509Certificate

Adds the `signatureAlgorithm` property to a X509Certificate allowing
users to retrieve a string representing the algorithm used to sign the
certificate. This string is defined by the OpenSSL library.

Fixes: nodejs/node#59103
PR-URL: nodejs/node#59235
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Filip Skokan <panva.ip@gmail.com>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>

Author: patrickrbc

include/ncrypto.h

@@ -1081,6 +1081,8 @@ class X509View final {
   BIOPointer getInfoAccess() const;
   BIOPointer getValidFrom() const;
   BIOPointer getValidTo() const;
+  std::optional<std::string_view> getSignatureAlgorithm() const;
+  std::optional<std::string> getSignatureAlgorithmOID() const;
   int64_t getValidFromTime() const;
   int64_t getValidToTime() const;
   DataPointer getSerialNumber() const;

src/ncrypto.cpp

@@ -17,7 +17,9 @@
 #endif
 
 #include <algorithm>
+#include <array>
 #include <cstring>
+#include <string_view>
 #if OPENSSL_VERSION_MAJOR >= 3
 #include <openssl/core_names.h>
 #include <openssl/params.h>
@@ -1106,6 +1108,29 @@ BIOPointer X509View::getValidTo() const {
   return bio;
 }
 
+std::optional<std::string_view> X509View::getSignatureAlgorithm() const {
+  if (cert_ == nullptr) return std::nullopt;
+  int nid = X509_get_signature_nid(cert_);
+  if (nid == NID_undef) return std::nullopt;
+  const char* ln = OBJ_nid2ln(nid);
+  if (ln == nullptr) return std::nullopt;
+  return std::string_view(ln);
+}
+
+std::optional<std::string> X509View::getSignatureAlgorithmOID() const {
+  if (cert_ == nullptr) return std::nullopt;
+  const X509_ALGOR* alg = nullptr;
+  X509_get0_signature(nullptr, &alg, cert_);
+  if (alg == nullptr) return std::nullopt;
+  const ASN1_OBJECT* obj = nullptr;
+  X509_ALGOR_get0(&obj, nullptr, nullptr, alg);
+  if (obj == nullptr) return std::nullopt;
+  std::array<char, 128> buf{};
+  int len = OBJ_obj2txt(buf.data(), buf.size(), obj, 1);
+  if (len < 0 || static_cast<size_t>(len) >= buf.size()) return std::nullopt;
+  return std::string(buf.data(), static_cast<size_t>(len));
+}
+
 int64_t X509View::getValidToTime() const {
 #ifdef OPENSSL_IS_BORINGSSL
 #ifndef NCRYPTO_NO_ASN1_TIME