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FLASHING.md says how to take a newer version of the colleague's tree (copy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

@@ -0,0 +1,54 @@
+#pragma once
+
+#include "keys.hpp"
+#include <vanetza/common/byte_buffer.hpp>
+#include <vanetza/security/hash_algorithm.hpp>
+#include <string>
+
+namespace vanetza
+{
+namespace pki
+{
+
+class Certificate;
+class EncryptedData;
+class SecurityModule;
+
+using security::HashAlgorithm;
+
+/**
+ * \brief Parameters for an InnerEcRequest / outer EtsiTs103097Data-Signed enrolment message.
+ * \see TS 102 941 §6.2.3.2
+ */
+struct EnrolmentRequestParameters
+{
+    std::string its_id; // canonical id (initial) or current EC HashedId8 (re-enrolment)
+    PublicKey verification_key; // to be certified; private key in SecurityModule for POP signature
+    PublicKey outer_signer_key; // signs outer Data-Signed; canonical key (initial) or current EC verification key (re-enrolment)
+    HashAlgorithm hash_algo = HashAlgorithm::SHA256; // POP and outer signatures
+    const Certificate* outer_signer_certificate = nullptr; // null → signer=self; non-null → signer=digest of this cert
+};
+
+/**
+ * \brief Build the signed (but not yet encrypted) enrolment request payload.
+ *
+ * Layered signatures: outer EtsiTs103097Data-Signed (signed with outer_signer_key;
+ * signer=self for initial enrolment, digest(outer_signer_certificate) for re-keying)
+ * wraps EtsiTs102941Data{enrolmentRequest=InnerEcRequestSignedForPop}, which is
+ * the OER-encoded InnerEcRequest signed with verification_key (signer=self) as POP.
+ * Exposed for testing; production code should call build_enrolment_request().
+ */
+ByteBuffer build_signed_enrolment_request(SecurityModule& security, const EnrolmentRequestParameters& parameters);
+
+/**
+ * \brief Build the EA-encrypted enrolment request.
+ *
+ * Call .encode() on the result for the OER bytes to POST. The ECIES context
+ * held in the returned EncryptedData is also needed to decrypt the EA's
+ * response (same symmetric key via pskRecipInfo).
+ */
+EncryptedData build_enrolment_request(SecurityModule& security, const EnrolmentRequestParameters& parameters,
+    const Certificate& ea_certificate);
+
+} // namespace pki
+} // namespace vanetza