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+<code C++ main.cpp>
+#include <Arduino.h>
+#include <WiFi.h>
+#include <WiFiClientSecure.h>
+#include <HTTPClient.h>
+#include <pgmspace.h>
+// ===================== LAB CONFIG =====================
+// Wi-Fi credentials
+const char* WIFI_SSID     = "LAB_WIFI_SSID";
+const char* WIFI_PASSWORD = "LAB_WIFI_PASSWORD";
+// Server hostname and port.
+// Hostname MUST match the CN/SAN in your server certificate (e.g. "iot-lab.local").
+const char* SERVER_HOST   = "iot-lab.local";
+const uint16_t SERVER_PORT = 8443;
+// URL used by HTTPClient (hostname + port + path)
+const char* SERVER_URL    = "https://iot-lab.local:8443/ingest";
+// Device identity
+const char* DEVICE_ID     = "sparrow-01";
+// MAC secret key – must match SECRET_KEY in secure_server.py
+const char* SECRET_KEY    = "LAB2_SUPER_SECRET_MAC_KEY";
+// Root CA certificate (PEM), copied from ca.crt.
+// Replace the placeholder contents with your actual CA cert.
+static const char LAB_ROOT_CA[] PROGMEM = R"EOF(
+-----BEGIN CERTIFICATE-----
+PASTE_YOUR_CA_CERT_HERE
+-----END CERTIFICATE-----
+)EOF";
+// ======================================================
+WiFiClientSecure secureClient;
+// Very simple, non-cryptographic MAC, must match server's compute_mac()
+uint32_t computeMac(const String& payload, const char* secret) {
+  String data = payload + secret;
+  uint32_t h = 0;
+  for (size_t i = 0; i < data.length(); i++) {
+    uint8_t b = static_cast<uint8_t>(data[i]);
+    h = (h * 31) ^ b;
+  }
+  return h;
+}
+void connectToWiFi() {
+  Serial.printf("Connecting to WiFi SSID: %s\n", WIFI_SSID);
+  WiFi.mode(WIFI_STA);
+  WiFi.begin(WIFI_SSID, WIFI_PASSWORD);
+  uint8_t retries = 0;
+  while (WiFi.status() != WL_CONNECTED && retries < 30) {
+    delay(500);
+    Serial.print(".");
+    retries++;
+  }
+  if (WiFi.status() == WL_CONNECTED) {
+    Serial.println("\nWiFi connected!");
+    Serial.print("IP address: ");
+    Serial.println(WiFi.localIP());
+  } else {
+    Serial.println("\nFailed to connect to WiFi");
+  }
+}
+void setup() {
+  Serial.begin(115200);
+  delay(2000);
+  connectToWiFi();
+  secureClient.setTimeout(15000);
+  // Load CA certificate so the ESP32 can verify the server's cert.
+  if (!secureClient.setCACert(LAB_ROOT_CA)) {
+    Serial.println("Failed to load CA certificate!");
+  } else {
+    Serial.println("CA certificate loaded.");
+  }
+  randomSeed(esp_random());
+}
+void loop() {
+  if (WiFi.status() != WL_CONNECTED) {
+    Serial.println("WiFi disconnected, reconnecting...");
+    connectToWiFi();
+  }
+  if (WiFi.status() == WL_CONNECTED) {
+    // Fake sensor data (same ranges as before)
+    float tempC     = 20.0 + (random(0, 1000) / 100.0f);  // 20.00–29.99
+    float humidity  = 40.0 + (random(0, 1000) / 50.0f);   // 40.0–59.9
+    int   battery   = random(60, 100);                    // 60–99 %
+    // Build JSON WITHOUT MAC first, in canonical key order:
+    // battery, device_id, humidity, temp_c
+    // This must match the server's json.dumps(sort_keys=True,separators=(",",":"))
+    String jsonNoMac = "{";
+    jsonNoMac += "\"battery\":" + String(battery) + ",";
+    jsonNoMac += "\"device_id\":\"" + String(DEVICE_ID) + "\",";
+    jsonNoMac += "\"humidity\":" + String(humidity, 1) + ",";
+    jsonNoMac += "\"temp_c\":" + String(tempC, 2);
+    jsonNoMac += "}";
+    // Compute MAC over jsonNoMac + SECRET_KEY
+    uint32_t mac = computeMac(jsonNoMac, SECRET_KEY);
+    // Full JSON payload including MAC
+    String payload = "{";
+    payload += "\"battery\":" + String(battery) + ",";
+    payload += "\"device_id\":\"" + String(DEVICE_ID) + "\",";
+    payload += "\"humidity\":" + String(humidity, 1) + ",";
+    payload += "\"temp_c\":" + String(tempC, 2) + ",";
+    payload += "\"mac\":" + String(mac);
+    payload += "}";
+    Serial.println("Sending HTTPS POST to server (with cert validation)...");
+    Serial.println("URL: " + String(SERVER_URL));
+    Serial.println("Payload: " + payload);
+    HTTPClient http;
+    // Begin HTTPS connection with certificate verification.
+    if (!http.begin(secureClient, SERVER_URL)) {
+      Serial.println("Failed to start HTTP connection");
+    } else {
+      http.addHeader("Content-Type", "application/json");
+      int httpCode = http.POST(payload);
+      if (httpCode > 0) {
+        Serial.printf("HTTP response code: %d\n", httpCode);
+        String response = http.getString();
+        Serial.println("Response body: " + response);
+      } else {
+        Serial.printf("HTTP POST failed, error: %s\n", http.errorToString(httpCode).c_str());
+      }
+      Serial.println("-----------------------------");
+      http.end();
+    }
+  }
+  delay(5000);  // send every 5 seconds
+}
+</code>