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FLASHING.md says how to take a newer version of the colleague's tree (copy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

@@ -0,0 +1,54 @@
+#pragma once
+
+#include "certificate.hpp"
+#include "response_codes.hpp"
+#include <vanetza/common/byte_buffer.hpp>
+#include <boost/optional/optional.hpp>
+
+namespace vanetza
+{
+namespace pki
+{
+
+class SecurityModule;
+
+// Result of parsing a decrypted AuthorizationResponse payload as specified
+// in ETSI TS 102 941 §6.2.3.3.2.
+struct AuthorizationResponse
+{
+    // Response code from InnerAtResponse. Parsing succeeds regardless of
+    // the code value; the caller decides how to act on non-ok results.
+    AuthorizationResponseCode code;
+
+    // requestHash from InnerAtResponse (SHA-256 prefix of the request).
+    ByteBuffer request_hash;
+
+    // New Authorization Ticket returned by the AA. Present iff the parser
+    // was able to decode a certificate; the caller must still check that
+    // `code` is `ok` before relying on it.
+    boost::optional<Certificate> certificate;
+};
+
+/**
+ * Parse a decrypted AuthorizationResponse per TS 102 941 §6.2.3.3.2.
+ *
+ * Verifies:
+ *   - outer Ieee1609Dot2Data is signedData
+ *   - signer = digest, matching HashedId8(aa_certificate)
+ *   - tbsData.headerInfo.psid == aid::SCR
+ *   - outer signature verifies against aa_certificate
+ *   - inner EtsiTs102941Data.version == v1
+ *   - inner content variant is authorizationResponse
+ *
+ * If `code == ok` the message MUST carry a certificate per TS 102 941;
+ * for non-ok codes the parser returns normally with whatever certificate
+ * (if any) was provided.
+ *
+ * \throws DecodingFailure on structural failure or missing required certificate
+ * \throws VerificationFailure on signer-digest or signature mismatch
+ */
+AuthorizationResponse parse_authorization_response(SecurityModule& security, const ByteBuffer& decrypted,
+    const Certificate& aa_certificate);
+
+} // namespace pki
+} // namespace vanetza