test: Add support for TLS v1.3 version check

For compatibility purposes, it is not possible to directly check the
version in handshake to determine if TLSv1.3 is currently in use.

The best practice in the RFC is to check the supported_versions
extension to see if it supports TLSv1.3.

test/handshake_test.cpp

@@ -616,7 +616,29 @@ TEST_CASE("ssl/tls versions") {
                                 [&buffer, &server_stream, &version](const error_code&, std::size_t length) {
                                   tls_record rec(net::buffer(buffer, length));
                                   REQUIRE(rec.type == tls_record::record_type::handshake);
-                                  CHECK(rec.version == version);
+                                  if (version != tls_version::tls_1_3) {
+                                    CHECK(rec.version == version);
+                                  } else {
+                                    bool support_tls_v1_3 = false;
+
+                                    if (rec.type == tls_record::record_type::handshake) {
+                                      tls_handshake& handshake = variant::get<tls_handshake>(rec.message);
+                                      auto& extension = variant::get<tls_handshake::client_hello>(handshake.message).extension;
+
+                                      auto it = std::find_if(extension.begin(), extension.end(), [](const tls_extension& s) {
+                                        return s.type == tls_extension::extension_type::supported_versions;
+                                      });
+
+                                      if (it != extension.end()) {
+                                        auto& versions = variant::get<tls_extension::supported_versions>(it->message).version;
+                                        support_tls_v1_3 = std::any_of(versions.begin(), versions.end(), [](const auto& s) {
+                                          return s == tls_version::tls_1_3;
+                                        });
+                                      }
+                                    }
+
+                                    REQUIRE(support_tls_v1_3);
+                                  }
                                   server_stream.close();
                                 });