Keep the colleague's microbu-esp32c5 tree in this repository

obu-firmware builds against vanetza-idf from microbu-esp32c5/external, but
that tree was gitignored, so a clone of this repository could not build the
firmware it ships. It is now committed here as ordinary files in its own
folder, microbu-esp32c5/: the colleague's commit cf4b99f plus the V2X2MAP
bridge's signature verification (--trust) used on the bench. Nothing is
fetched from or pushed to the colleague's repository; this repository and
its remotes carry everything. The folder's own .gitignore keeps build output,
downloaded components and private key material out, as it did there; the
committed file set is identical to that repository's tracked files.

The ESP32-C5 is still flashed from obu-firmware/, which only takes
vanetza-idf from microbu-esp32c5/, so the two stay separate folders.
FLASHING.md says how to take a newer version of the colleague's tree (copy
it over the folder, rebuild, test, commit).

microbu-esp32c5/external/vanetza-idf/vanetza/security/v2/subject_attribute.hpp

@@ -0,0 +1,192 @@
+#ifndef SUBJECT_ATTRIBUTE_HPP_IRZLEB7C
+#define SUBJECT_ATTRIBUTE_HPP_IRZLEB7C
+
+#include <vanetza/security/v2/int_x.hpp>
+#include <vanetza/security/v2/public_key.hpp>
+#include <vanetza/security/v2/serialization.hpp>
+#include <boost/variant/variant.hpp>
+#include <cstdint>
+#include <list>
+
+namespace vanetza
+{
+namespace security
+{
+namespace v2
+{
+
+/// SubjectAssurance specified in TS 103 097 v1.2.1 in section 6.6 and 7.4.1
+struct SubjectAssurance
+{
+    SubjectAssurance(uint8_t _raw = 0) : raw(_raw) {}
+
+    static constexpr uint8_t assurance_mask = 0xE0;
+    static constexpr uint8_t confidence_mask = 0x03;
+
+    uint8_t raw;
+
+    uint8_t assurance() const
+    {
+        return (raw & assurance_mask) >> 5;
+    }
+
+    uint8_t confidence() const
+    {
+        return raw & confidence_mask;
+    }
+};
+
+/// ItsAidSsp specified in TS 103 097 v1.2.1, section 6.9
+struct ItsAidSsp
+{
+    IntX its_aid;
+    ByteBuffer service_specific_permissions;
+};
+
+/// SubjectAttributeType specified in TS 103 097 v1.2.1, section 6.5
+enum class SubjectAttributeType : uint8_t {
+    Verification_Key = 0,       //VerificationKey
+    Encryption_Key = 1,         //EncryptionKey
+    Assurance_Level = 2,        //SubjectAssurance
+    Reconstruction_Value = 3,   //EccPoint
+    ITS_AID_List = 32,          //std::list<IntX>
+    ITS_AID_SSP_List = 33,      //std::list<ItsAidSsp>
+};
+
+/// VerificationKey specified in TS 103 097 v1.2.1, section 6.4
+struct VerificationKey
+{
+    PublicKey key;
+};
+
+/// EncryptionKey specified in TS 103 097 v1.2.1, section 6.4
+struct EncryptionKey
+{
+    PublicKey key;
+};
+
+/// SubjectAttribute specified in TS 103 097 v1.2.1, section 6.4
+using SubjectAttribute = boost::variant<
+    VerificationKey,
+    EncryptionKey,
+    SubjectAssurance,
+    EccPoint,
+    std::list<IntX>,
+    std::list<ItsAidSsp>
+>;
+
+/**
+ * \brief Determines SubjectAttributeType to a given SubjectAttribute
+ * \param attribute
+ * \return type
+ */
+SubjectAttributeType get_type(const SubjectAttribute&);
+
+/**
+ * \brief Calculates size of a SubjectAttribute
+ * \param sub
+ * \return number of octets needed to serialize the SubjectAttribute
+ */
+size_t get_size(const SubjectAttribute&);
+
+/**
+ * \brief Calculates size of a SubjectAssurance
+ * \param sub
+ * \return number of octets needed to serialize the SubjectAssurance
+ */
+size_t get_size(const SubjectAssurance&);
+
+/**
+ * \brief Calculates size of an ItsAidSsp
+ * \param its_aid_ssp
+ * \return number of octets needed to serialize the ItsAidSsp
+ */
+size_t get_size(const ItsAidSsp&);
+
+/**
+ * \brief Deserializes a SubjectAttribute from a binary archive
+ * \param ar with a serialized SubjectAttribute at the beginning
+ * \param sub to deserialize
+ * \return size of the deserialized SubjectAttribute
+ */
+size_t deserialize(InputArchive&, SubjectAttribute&);
+
+/**
+ * \brief Deserializes an ItsAidSsp from a binary archive
+ * \param ar with a serialized ItsAidSsp at the beginning
+ * \param its_aid_ssp to deserialize
+ * \return size of the deserialized ItsAidSsp
+ */
+size_t deserialize(InputArchive&, ItsAidSsp&);
+
+/**
+ * \brief Serializes a SubjectAttribute into a binary archive
+ * \param ar to serialize in
+ * \param sub to serialize
+ */
+void serialize(OutputArchive&, const SubjectAttribute&);
+
+/**
+ * \brief Serializes an ItsAidSsp into a binary archive
+ * \param ar to serialize in
+ * \param its_aid_ssp to serialize
+ */
+void serialize(OutputArchive&, const ItsAidSsp&);
+
+namespace detail
+{
+
+template<SubjectAttributeType>
+struct subject_attribute_type;
+
+template<>
+struct subject_attribute_type<SubjectAttributeType::Verification_Key>
+{
+    using type = VerificationKey;
+};
+
+template<>
+struct subject_attribute_type<SubjectAttributeType::Encryption_Key>
+{
+    using type = EncryptionKey;
+};
+
+template<>
+struct subject_attribute_type<SubjectAttributeType::Assurance_Level>
+{
+    using type = SubjectAssurance;
+};
+
+template<>
+struct subject_attribute_type<SubjectAttributeType::Reconstruction_Value>
+{
+    using type = EccPoint;
+};
+
+template<>
+struct subject_attribute_type<SubjectAttributeType::ITS_AID_List>
+{
+    using type = std::list<IntX>;
+};
+
+template<>
+struct subject_attribute_type<SubjectAttributeType::ITS_AID_SSP_List>
+{
+    using type = std::list<ItsAidSsp>;
+};
+
+} // namespace detail
+
+/**
+ * \brief resolve type for matching SubjectAttributeType
+ *
+ * This is kind of the reverse function of get_type(const SubjectAttribute&)
+ */
+template<SubjectAttributeType T>
+using subject_attribute_type = typename detail::subject_attribute_type<T>::type;
+
+} // namespace v2
+} // namespace security
+} // namespace vanetza
+
+#endif /* SUBJECT_ATTRIBUTE_HPP_IRZLEB7C */