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+<code C++ main.cpp>
+#include <Arduino.h>
+#include <WiFi.h>
+#include <WiFiClientSecure.h>
+#include <HTTPClient.h>
+// ====== LAB CONFIG: fill these in per-lab ======
+const char* WIFI_SSID     = "LAB_WIFI_SSID";
+const char* WIFI_PASSWORD = "LAB_WIFI_PASSWORD";
+// Replace with your server's IP
+const char* SERVER_URL    = "https://192.168.1.100:8443/ingest";
+const char* DEVICE_ID     = "sparrow-01";
+// This key must match SECRET_KEY on the server
+// NOTE: in real systems, putting secrets in firmware has risks → discussion later.
+const char* SECRET_KEY    = "LAB2_SUPER_SECRET_MAC_KEY";
+// ===============================================
+WiFiClientSecure secureClient;
+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");
+  }
+}
+// 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 setup() {
+  Serial.begin(115200);
+  delay(2000);
+  connectToWiFi();
+  // HTTPS client config:
+  secureClient.setTimeout(15000);
+  // For the lab, we disable certificate validation to keep
+  // the code simple. This gives confidentiality but not strong
+  // authenticity → good discussion point.
+  secureClient.setInsecure();  // DO NOT DO THIS IN REAL PRODUCTS
+  randomSeed(esp_random());
+}
+void loop() {
+  if (WiFi.status() != WL_CONNECTED) {
+    Serial.println("WiFi disconnected, reconnecting...");
+    connectToWiFi();
+  }
+  if (WiFi.status() == WL_CONNECTED) {
+    // Fake sensor data, like in Lab 1
+    float tempC     = 20.0 + (random(0, 1000) / 100.0f);
+    float humidity  = 40.0 + (random(0, 1000) / 50.0f);
+    int   battery   = random(60, 100);
+    // Build JSON without MAC first
+    // We'll use this version to compute MAC both here and on the server.
+    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
+    uint32_t mac = computeMac(jsonNoMac, SECRET_KEY);
+    // Full JSON payload with 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...");
+    Serial.println("URL: " + String(SERVER_URL));
+    Serial.println("Payload (with MAC): " + payload);
+    HTTPClient http;
+    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);
+      String response = http.getString();
+      Serial.printf("HTTP response code: %d\n", httpCode);
+      Serial.println("Response body: " + response);
+      Serial.println("-----------------------------");
+      http.end();
+    }
+  }
+  delay(5000);
+}
+</code>