Keep vanetza-idf in obu-firmware, so a plain clone builds the firmware

obu-firmware builds against the vanetza-idf C-ITS library, which until now
came from the colleague's microbu-esp32c5 tree beside the repository and was
not tracked here, so a clone of this repository could not build the firmware
it ships. The library alone is now part of obu-firmware, as
obu-firmware/external/vanetza-idf: their external/vanetza-idf at commit
cf4b99f, unchanged (9775 files; see its PROVENANCE.md). CMake takes it from
there by default; -DVANETZA_IDF_DIR still points the build elsewhere.

The rest of the colleague's tree (their own VAM firmware, PKI tooling,
station-link Python tools, the V2X2MAP bridge) stays out of this repository
and gitignored; nothing is pushed to their repository. NOTES.md, docs/06,
TODO.md and the pcap verifier's usage line point at the new location.

obu-firmware/external/vanetza-idf/vanetza/security/sign_service.hpp

@@ -0,0 +1,79 @@
+#ifndef SIGN_SERVICE_HPP_4MDQBSEF
+#define SIGN_SERVICE_HPP_4MDQBSEF
+
+#include <vanetza/common/byte_buffer.hpp>
+#include <vanetza/common/its_aid.hpp>
+#include <vanetza/common/position_provider.hpp>
+#include <vanetza/net/packet.hpp>
+#include <vanetza/security/hash_algorithm.hpp>
+#include <vanetza/security/key_type.hpp>
+#include <vanetza/security/secured_message.hpp>
+#include <vanetza/security/signing_policy.hpp>
+#include <boost/optional/optional.hpp>
+#include <functional>
+
+namespace vanetza
+{
+
+// forward declaration
+class Runtime;
+
+namespace security
+{
+
+// mandatory SN-SIGN.request parameters
+struct SignRequest
+{
+    DownPacket plain_message;
+    ItsAid its_aid;
+    ByteBuffer permissions;
+    // optional SN-ENCAP.request context_information (TS 102 723-8 V1.1.1 Table 24):
+    // opaque octets for selecting properties of the security protocol
+    ByteBuffer context_information;
+    bool external_payload = false;
+    bool self_signed = false;
+};
+
+enum class SignConfirmError
+{
+    Unspecified,
+    No_Certificate,
+    No_Service,
+};
+
+// mandatory SN-SIGN.confirm parameters
+struct SignConfirm
+{
+    SignConfirm(SignConfirmError error, boost::optional<SecuredMessage> message)
+        : error(error), secured_message(std::move(message))
+    {
+    }
+
+    static SignConfirm success(SecuredMessage&& message)
+    {
+        return { SignConfirmError::Unspecified, std::move(message) };
+    }
+
+    static SignConfirm failure(SignConfirmError error)
+    {
+        return { error, boost::none };
+    }
+
+    SignConfirmError error;
+    boost::optional<SecuredMessage> secured_message;
+};
+
+/**
+ * Equivalant of SN-SIGN service in TS 102 723-8 v1.1.1
+ */
+class SignService
+{
+public:
+    virtual ~SignService() = default;
+    virtual SignConfirm sign(SignRequest&&) = 0;
+};
+
+} // namespace security
+} // namespace vanetza
+
+#endif /* SIGN_SERVICE_HPP_4MDQBSEF */