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FLASHING.md says how to take a newer version of the colleague's tree (copy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/header_field.hpp

@@ -0,0 +1,144 @@
+#ifndef HEADER_FIELD_HPP_IHIAKD4K
+#define HEADER_FIELD_HPP_IHIAKD4K
+
+#include <vanetza/security/v2/basic_elements.hpp>
+#include <vanetza/security/v2/certificate.hpp>
+#include <vanetza/security/v2/encryption_parameter.hpp>
+#include <vanetza/security/v2/int_x.hpp>
+#include <vanetza/security/v2/recipient_info.hpp>
+#include <vanetza/security/v2/region.hpp>
+#include <vanetza/security/v2/signer_info.hpp>
+#include <boost/variant/variant.hpp>
+#include <list>
+
+namespace vanetza
+{
+namespace security
+{
+namespace v2
+{
+
+/// HeaderFieldType specified in TS 103 097 v1.2.1, section 5.5
+enum class HeaderFieldType : uint8_t
+{
+    Generation_Time = 0,                    // Time64
+    Generation_Time_Confidence = 1,         // Time64WithStandardDeviation
+    Expiration = 2,                         // Time32
+    Generation_Location = 3,                // TreeDLocation
+    Request_Unrecognized_Certificate = 4,   // std::list<HashedId3>
+    Its_Aid = 5,                            // IntX
+    Signer_Info = 128,                      // SignerInfo
+    Encryption_Parameters = 129,            // EncryptionParameters
+    Recipient_Info = 130,                   // std::list<RecipientInfo>
+};
+
+/// HeaderField specified in TS 103 097 v1.2.1, section 5.4
+using HeaderField = boost::variant<
+    Time64,
+    Time64WithStandardDeviation,
+    Time32,
+    ThreeDLocation,
+    std::list<HashedId3>,
+    IntX,
+    SignerInfo,
+    EncryptionParameter,
+    std::list<RecipientInfo>
+>;
+
+/**
+ * \brief Determines HeaderFieldType to a given HeaderField
+ * \param field
+ * \return type
+ */
+HeaderFieldType get_type(const HeaderField& field);
+
+/**
+ * \brief Calculates size of a HeaderField
+ * \param field
+ * \return number of octets needed to serialize the HeaderField
+ */
+std::size_t get_size(const HeaderField& field);
+
+/**
+ * \brief Serializes a HeaderField into a binary archive
+ * \note Serialization of HeaderField lists is provided by template
+ * \param ar to serialize in
+ * \param field to serialize
+ */
+void serialize(OutputArchive& ar, const HeaderField& field);
+
+/**
+ * \brief Deserializes a list of HeaderFields from a binary archive
+ * \param ar with a serialized list of HeaderFields at the beginning
+ * \param list of HeaderFields to deserialize
+ * \return size of the deserialized list
+ */
+size_t deserialize(InputArchive& ar, std::list<HeaderField>& list);
+
+/**
+ * \brief resolve type for matching HeaderFieldType
+ *
+ * This is kind of the reverse function of get_type(const HeaderField&)
+ */
+template<HeaderFieldType>
+struct header_field_type;
+
+template<>
+struct header_field_type<HeaderFieldType::Generation_Time>
+{
+    using type = Time64;
+};
+
+template<>
+struct header_field_type<HeaderFieldType::Generation_Time_Confidence>
+{
+    using type = Time64WithStandardDeviation;
+};
+
+template<>
+struct header_field_type<HeaderFieldType::Expiration>
+{
+    using type = Time32;
+};
+
+template<>
+struct header_field_type<HeaderFieldType::Generation_Location>
+{
+    using type = ThreeDLocation;
+};
+
+template<>
+struct header_field_type<HeaderFieldType::Request_Unrecognized_Certificate>
+{
+    using type = std::list<HashedId3>;
+};
+
+template<>
+struct header_field_type<HeaderFieldType::Its_Aid>
+{
+    using type = IntX;
+};
+
+template<>
+struct header_field_type<HeaderFieldType::Signer_Info>
+{
+    using type = SignerInfo;
+};
+
+template<>
+struct header_field_type<HeaderFieldType::Encryption_Parameters>
+{
+    using type = EncryptionParameter;
+};
+
+template<>
+struct header_field_type<HeaderFieldType::Recipient_Info>
+{
+    using type = std::list<RecipientInfo>;
+};
+
+} // namespace v2
+} // namespace security
+} // namespace vanetza
+
+#endif /* HEADER_FIELD_HPP_IHIAKD4K */