feat: dashboard token auth + README v2/v3 payload sections split

Dashboard:
- Optional DASHBOARD_TOKEN env var (K8s secret 'snek-dashboard-secret')
- Flask before_request check via Authorization header or ?token= param
- /webhook and /healthz remain public (SNEK POST needs to reach webhook)
- Frontend prompts for token on first load, stores in localStorage
- Token forwarded on fetch() calls and EventSource URL

README decoding section:
- Split into two full sub-sections for Sens'it Discovery (v3) and Sens'it v2
- Explicit bit ordering note (MSB-LSB v3 vs LSB-MSB v2)
- Byte-by-byte tables, formulas per mode, worked examples
- Note that auto-detection uses byte 0 bits 2-0 == 0b110 marker for v3

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

dashboard/app.py

@@ -15,8 +15,24 @@ from sensit_decoder import decode as sensit_decode
 DB_PATH = os.environ.get("DB_PATH", "/data/messages.db")
 Path(DB_PATH).parent.mkdir(parents=True, exist_ok=True)
 
+TOKEN = os.environ.get("DASHBOARD_TOKEN", "").strip()
+PUBLIC_ROUTES = {"/webhook", "/healthz"}
+
 app = Flask(__name__, static_folder="static", static_url_path="/static")
 
+
+@app.before_request
+def _check_token():
+    if not TOKEN or request.path in PUBLIC_ROUTES:
+        return None
+    supplied = (
+        request.headers.get("Authorization", "").removeprefix("Bearer ").strip()
+        or request.args.get("token", "").strip()
+    )
+    if supplied != TOKEN:
+        return jsonify({"error": "unauthorized"}), 401
+    return None
+
 # --- SSE broadcast ---
 _subscribers: list[queue.Queue] = []
 _subscribers_lock = threading.Lock()

dashboard/static/index.html

@@ -73,6 +73,35 @@
 </div>
 
 <script>
+// --- Token gate --------------------------------------------------------------
+const TOKEN_KEY = 'snek_dashboard_token';
+let token = localStorage.getItem(TOKEN_KEY) || '';
+
+async function ensureToken() {
+  // Probe if the server requires a token
+  const probe = await fetch('/api/devices', { headers: authHeaders() });
+  if (probe.ok) return;
+  if (probe.status !== 401) return;
+  while (true) {
+    const t = window.prompt('Access token');
+    if (t === null) return;
+    const r = await fetch('/api/devices', { headers: { Authorization: 'Bearer ' + t } });
+    if (r.ok) {
+      token = t.trim();
+      localStorage.setItem(TOKEN_KEY, token);
+      return;
+    }
+  }
+}
+
+function authHeaders() {
+  return token ? { Authorization: 'Bearer ' + token } : {};
+}
+
+function authQuery() {
+  return token ? '?token=' + encodeURIComponent(token) : '';
+}
+
 const state = { messagesByDevice: {}, chart: null, selectedDevice: null };
 
 const fmtTime = ts => new Date(ts * 1000).toLocaleString('fr-FR', { day: '2-digit', month: '2-digit', year: 'numeric', hour: '2-digit', minute: '2-digit' });
@@ -286,7 +315,7 @@ function renderChart() {
 }
 
 async function bootstrap() {
-  const r = await fetch('/api/messages?limit=200');
+  const r = await fetch('/api/messages?limit=200', { headers: authHeaders() });
   const msgs = await r.json();
   msgs.forEach(m => {
     if (!state.messagesByDevice[m.device]) state.messagesByDevice[m.device] = [];
@@ -298,7 +327,7 @@ async function bootstrap() {
 }
 
 function connectSSE() {
-  const es = new EventSource('/events');
+  const es = new EventSource('/events' + authQuery());
   es.onmessage = (ev) => {
     try {
       const msg = JSON.parse(ev.data);
@@ -317,7 +346,7 @@ document.getElementById('chart-device').addEventListener('change', (e) => {
   renderChart();
 });
 
-bootstrap().then(connectSSE);
+ensureToken().then(bootstrap).then(connectSSE);
 </script>
 </body>
 </html>