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FLASHING.md says how to take a newer version of the colleague's tree (copy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

@@ -0,0 +1,66 @@
+#pragma once
+
+#include "keys.hpp"
+#include "psid_ssp.hpp"
+#include <vanetza/common/byte_buffer.hpp>
+#include <vanetza/common/clock.hpp>
+#include <vanetza/security/hash_algorithm.hpp>
+#include <boost/optional/optional.hpp>
+#include <chrono>
+#include <list>
+
+namespace vanetza
+{
+namespace pki
+{
+
+class Certificate;
+class EncryptedData;
+class SecurityModule;
+
+using security::HashAlgorithm;
+
+/**
+ * \brief Hint for sharedAtRequest.requestedSubjectAttributes.validityPeriod.
+ * \see IEEE 1609.2 Time32 / Duration::hours
+ */
+struct ValidityPeriodHint
+{
+    Clock::time_point start;
+    std::chrono::hours duration;
+};
+
+/**
+ * \brief Parameters for an AuthorizationRequest (encryptedEcSignature variant).
+ * \see TS 102 941 §6.2.3.3.1
+ */
+struct AuthorizationRequestParameters
+{
+    const Certificate* ec = nullptr; // current EC, signs the inner EC proof; mandatory
+    const Certificate* ea_certificate = nullptr; // recipient of encryptedEcSignature; mandatory
+    const Certificate* aa_certificate = nullptr; // recipient of outer encryption; mandatory
+    PublicKey verification_key; // fresh key to be certified; private key in SecurityModule; mandatory
+    boost::optional<PublicKey> at_encryption_key; // optional encryption key embedded in the AT
+    std::list<PsidSsp> permissions; // requested PSID/SSP set; must be non-empty
+    HashAlgorithm hash_algo = HashAlgorithm::SHA256; // EC proof and extDataHash; SHA-256 only
+    boost::optional<ValidityPeriodHint> validity_period; // optional; AA decides within CP §7.2.1 bounds
+    bool include_pop = true; // send AuthorizationRequestMessageWithPop; required by deployed AAs
+};
+
+/**
+ * \brief Build the inner EtsiTs102941Data{authorizationRequest} plaintext.
+ *
+ * Exposed for testing; production code should call build_authorization_request().
+ */
+ByteBuffer build_signed_authorization_request(SecurityModule& security,
+    const AuthorizationRequestParameters& parameters);
+
+/**
+ * \brief Build the AA-encrypted authorization request.
+ *
+ * Call .encode() on the result for the OER bytes to POST as `application/x-its-request`.
+ */
+EncryptedData build_authorization_request(SecurityModule& security, const AuthorizationRequestParameters& parameters);
+
+} // namespace pki
+} // namespace vanetza