Dingtian input push: HTTP Digest auth + auto-config on assign

Secure the device→backend input push, and configure it automatically when the
admin assigns the device (no manual URL/secret entry).

Auth — HTTP Digest (chosen by hardware testing: the device can't push to a
self-signed HTTPS backend, but does Digest correctly; a URL token is sniffable/
logged):
- digest-auth.ts: MD5 qop=auth challenge/verify, single-use nonces (replay
  resistance). Password never crosses the wire.
- push route: Digest + source-IP allowlist; per-device pushUser/pushPassword from
  lane_devices. Still not behind the SPA cookie/CSRF auth (machine call). The
  signed event log remains the real anti-fraud guarantee.

Auto-config on assign:
- setup assign: for push-capable devices, generate Digest creds, call
  configureInputPush to write them + the push URLs to the device, store the creds
  (password not echoed back). net.ts derives the backend IP on the device's
  subnet (BACKEND_HOST_IP override).
- driver configureInputPush sets auth=2 + creds; PushConfig carries the creds.
- removed the earlier URL-token approach.

Two hard-won device-write bugs fixed in the driver:
- configApi now sets an explicit Content-Length — the device silently ignores
  chunked request bodies (Node's default without Content-Length), so every config
  write looked successful ({"status":0}) but did nothing. This was the root cause
  of the session's "writes don't apply" mystery.
- #writeConfig polls until the change is verified, retrying (the device reboots on
  apply; back-to-back writes were lost). The `pass` field caps at 31 chars, so the
  generated password is 24 hex chars.

Verified on hardware: assign auto-configures the device; all 4 inputs then push
with Digest auth, zero failures. wiki/device-input-flow updated.

apps/server/src/digest-auth.ts

@@ -0,0 +1,97 @@
+import { createHash, randomBytes, timingSafeEqual } from "node:crypto";
+import type { FastifyReply, FastifyRequest } from "fastify";
+
+// HTTP Digest auth (RFC 2617, MD5, qop=auth) — verified against the Dingtian
+// device, which CAN do Digest but CANNOT do HTTPS to a self-signed cert. On
+// this flat network Digest is the strongest available push auth: the password
+// is never sent (only a nonce-keyed hash). It is defence-in-depth; the signed
+// event log is the real anti-fraud guarantee. See wiki/concepts/device-input-flow.md.
+
+export const DIGEST_REALM = "parking";
+
+const md5 = (s: string) => createHash("md5").update(s).digest("hex");
+
+/** Nonces we've issued and not yet consumed (single-use → replay resistance). */
+const issuedNonces = new Map<string, number>(); // nonce → issuedAt (ms epoch is unavailable in scripts but fine at runtime)
+const NONCE_TTL_MS = 5 * 60_000;
+
+function issueNonce(): string {
+  const nonce = randomBytes(16).toString("hex");
+  issuedNonces.set(nonce, Date.now());
+  // opportunistic cleanup
+  if (issuedNonces.size > 1000) {
+    const cutoff = Date.now() - NONCE_TTL_MS;
+    for (const [n, t] of issuedNonces) if (t < cutoff) issuedNonces.delete(n);
+  }
+  return nonce;
+}
+
+function parseDigest(header: string): Record<string, string> {
+  const out: Record<string, string> = {};
+  const re = /(\w+)=(?:"([^"]*)"|([^,]*))/g;
+  let m: RegExpExecArray | null;
+  while ((m = re.exec(header))) out[m[1]!] = (m[2] ?? m[3] ?? "").trim();
+  return out;
+}
+
+function eq(a: string, b: string): boolean {
+  const ab = Buffer.from(a);
+  const bb = Buffer.from(b);
+  return ab.length === bb.length && timingSafeEqual(ab, bb);
+}
+
+export interface DigestCreds {
+  readonly user: string;
+  readonly password: string;
+}
+
+/**
+ * Verify a Digest Authorization header. Returns true on success. On failure (or
+ * a missing/expired header) sets a 401 challenge on `reply` and returns false —
+ * the caller should stop. `creds` is the device's stored push credentials.
+ */
+export function verifyDigest(
+  req: FastifyRequest,
+  reply: FastifyReply,
+  creds: DigestCreds,
+): boolean {
+  const header = req.headers["authorization"];
+
+  if (!header || !/^Digest /i.test(header)) {
+    challenge(reply);
+    return false;
+  }
+
+  const p = parseDigest(header.replace(/^Digest /i, ""));
+  // Nonce must be one we issued and not yet consumed (single-use).
+  const issuedAt = p.nonce ? issuedNonces.get(p.nonce) : undefined;
+  if (!p.nonce || issuedAt === undefined || Date.now() - issuedAt > NONCE_TTL_MS) {
+    challenge(reply, true);
+    return false;
+  }
+
+  const ha1 = md5(`${creds.user}:${DIGEST_REALM}:${creds.password}`);
+  const ha2 = md5(`${req.method}:${p.uri ?? req.url}`);
+  const expected =
+    p.qop === "auth"
+      ? md5(`${ha1}:${p.nonce}:${p.nc}:${p.cnonce}:${p.qop}:${ha2}`)
+      : md5(`${ha1}:${p.nonce}:${ha2}`);
+
+  if (!p.response || !eq(expected, p.response) || !eq(p.username ?? "", creds.user)) {
+    challenge(reply);
+    return false;
+  }
+
+  // Consume the nonce so it can't be replayed.
+  issuedNonces.delete(p.nonce);
+  return true;
+}
+
+function challenge(reply: FastifyReply, stale = false): void {
+  const nonce = issueNonce();
+  reply.header(
+    "www-authenticate",
+    `Digest realm="${DIGEST_REALM}", qop="auth", nonce="${nonce}", algorithm=MD5${stale ? ", stale=true" : ""}`,
+  );
+  reply.code(401).send("authentication required");
+}

apps/server/src/net.ts

@@ -0,0 +1,30 @@
+import { networkInterfaces } from "node:os";
+
+// Figure out which local IP a device should call back on. For input-push, the
+// device needs OUR address on ITS subnet — pick the local IPv4 interface whose
+// network contains the device's IP. Override with BACKEND_HOST_IP if the
+// auto-pick is wrong (e.g. multi-homed host). See wiki/concepts/device-input-flow.md.
+
+export function backendIpForDevice(deviceHost: string): string | null {
+  if (process.env.BACKEND_HOST_IP) return process.env.BACKEND_HOST_IP;
+
+  const ip = deviceHost.split(".").map(Number);
+  if (ip.length !== 4 || ip.some((o) => Number.isNaN(o))) return null;
+
+  for (const ifaces of Object.values(networkInterfaces())) {
+    for (const i of ifaces ?? []) {
+      if (i.family !== "IPv4" || i.internal) continue;
+      const addr = i.address.split(".").map(Number);
+      const mask = i.netmask.split(".").map(Number);
+      if (addr.length !== 4 || mask.length !== 4) continue;
+      const sameNet = ip.every((o, k) => (o & mask[k]!) === (addr[k]! & mask[k]!));
+      if (sameNet) return i.address;
+    }
+  }
+  return null;
+}
+
+/** Backend port the device should call (the server's listen port). */
+export function backendPort(): number {
+  return Number(process.env.PORT ?? 3000);
+}

apps/server/src/routes/devices.ts

@@ -1,54 +1,82 @@
-import type { FastifyInstance, FastifyRequest } from "fastify";
+import type { FastifyInstance, FastifyReply, FastifyRequest } from "fastify";
+import { eq, laneDevices, type Db } from "@parking/db";
 import { deviceEvents } from "../device-events.js";
+import { verifyDigest } from "../digest-auth.js";
 
 // Inbound device push endpoints. The Dingtian board's "Input Link URL" feature
 // HTTP-calls us when an input (button) fires — no polling. We translate the
 // push into an internal device event; the entry flow decides what to do
-// (print a ticket, then command the relay). See wiki/entities/dingtian-relay.md.
+// (print a ticket, then command the relay). See wiki/concepts/device-input-flow.md.
 //
-// AUTH: these are machine-to-machine calls FROM the device, which can't do the
-// SPA's cookie/CSRF auth. They are intentionally NOT behind requireRole. Trust
-// does NOT come from this request — every barrier open is a host decision
-// recorded as a signed event, so an out-of-band/forged open has no matching
-// signed event and shows up as an anomaly (see wiki/concepts/append-only-event-chain
-// and threat-model). A shared-secret check can be layered on later as
-// defence-in-depth; on a flat network it isn't the security boundary.
+// AUTH: HTTP Digest (the device can do Digest but not HTTPS-to-self-signed —
+// both tested on hardware). The password is never sent on the wire; the secret
+// is NOT in the URL. Per-device credentials live in lane_devices (written on
+// assign). This is defence-in-depth on a flat network; the signed event log is
+// the real anti-fraud guarantee (an open with no matching signed event is an
+// anomaly). Source-IP is also checked. NOT behind the SPA cookie/CSRF auth
+// (machine call from the device).
 
 interface InputParams {
   deviceId: string;
   n: string;
+  edge: string;
 }
 
-export async function deviceRoutes(app: FastifyInstance): Promise<void> {
-  // Dingtian input ON-edge push (button pressed). The device is configured
-  // (via input_link_url) to call this path for each input. GET or POST both
-  // accepted — the device's method is configurable; the URL carries the input.
-  const handler = (edge: "on" | "off") =>
-    async (req: FastifyRequest<{ Params: InputParams }>) => {
-      const { deviceId, n } = req.params;
-      const input = Number(n);
-      app.log.info(`[dingtian:${deviceId}] input ${input} ${edge} (push)`);
-      deviceEvents.emitInput({
-        driverId: "dingtian",
-        deviceId,
-        input,
-        edge,
-        at: new Date().toISOString(),
-        source: "push",
-      });
-      return { ok: true };
-    };
+interface DingtianDeviceConfig {
+  host?: string;
+  pushUser?: string;
+  pushPassword?: string;
+}
+
+function clientIp(req: FastifyRequest): string {
+  return req.ip.replace(/^::ffff:/, "");
+}
+
+export async function deviceRoutes(app: FastifyInstance, db: Db): Promise<void> {
+  const handle = async (req: FastifyRequest<{ Params: InputParams }>, reply: FastifyReply) => {
+    const { deviceId, n, edge } = req.params;
+
+    const row = await db.select().from(laneDevices).where(eq(laneDevices.id, deviceId)).get();
+    const cfg = row?.config as DingtianDeviceConfig | undefined;
+
+    // Unknown device / not a dingtian / no push creds / wrong source IP → 404.
+    if (
+      !row ||
+      row.driverId !== "dingtian" ||
+      !cfg?.pushUser ||
+      !cfg.pushPassword ||
+      !cfg.host ||
+      clientIp(req) !== cfg.host
+    ) {
+      app.log.warn(`rejected device push: device=${deviceId} ip=${clientIp(req)}`);
+      return reply.code(404).send({ error: "not found" });
+    }
+
+    // Digest auth — issues a 401 challenge on first hit; the device retries with
+    // the hashed response (verifyDigest sends the challenge + returns false).
+    if (!verifyDigest(req, reply, { user: cfg.pushUser, password: cfg.pushPassword })) {
+      return; // 401 already sent
+    }
+
+    const input = Number(n);
+    const ed = edge === "off" ? "off" : "on";
+    app.log.info(`[dingtian:${deviceId}] input ${input} ${ed} (push)`);
+    deviceEvents.emitInput({
+      driverId: "dingtian",
+      deviceId,
+      input,
+      edge: ed,
+      at: new Date().toISOString(),
+      source: "push",
+    });
+    return { ok: true };
+  };
 
   for (const method of ["GET", "POST"] as const) {
     app.route({
       method,
-      url: "/api/devices/dingtian/:deviceId/input/:n/on",
-      handler: handler("on"),
-    });
-    app.route({
-      method,
-      url: "/api/devices/dingtian/:deviceId/input/:n/off",
-      handler: handler("off"),
+      url: "/api/devices/dingtian/:deviceId/input/:n/:edge",
+      handler: handle,
     });
   }
 }

apps/server/src/routes/setup.ts

@@ -1,7 +1,8 @@
-import { randomUUID } from "node:crypto";
+import { randomBytes, randomUUID } from "node:crypto";
 import type { FastifyInstance } from "fastify";
 import { eq, laneDevices, setupState, type Db } from "@parking/db";
 import {
+  hasPushConfig,
   isDiscoverable,
   registerBuiltinDrivers,
   registry,
@@ -9,6 +10,7 @@ import {
   type DeviceCategory,
 } from "@parking/devices";
 import { requireRole } from "../auth.js";
+import { backendIpForDevice, backendPort } from "../net.js";
 
 // First-run setup API. The admin reads the driver catalog and assigns devices
 // per lane. See wiki/concepts/first-run-setup.md.
@@ -80,6 +82,10 @@ export async function setupRoutes(app: FastifyInstance, db: Db): Promise<void> {
 
   // Assign a device to a lane. Validates the chosen driver + config against the
   // registry before persisting; rejects unknown drivers / missing config.
+  // For push-capable devices (e.g. Dingtian), the backend generates a secret
+  // token, configures the device to HTTP-push input events to us (no manual URL
+  // entry by the admin), and stores the token so the push endpoint can verify
+  // it. See wiki/concepts/device-input-flow.md.
   app.post<{ Body: AssignBody }>(
     "/api/setup/assign",
     { preHandler: adminGuard },
@@ -89,21 +95,60 @@ export async function setupRoutes(app: FastifyInstance, db: Db): Promise<void> {
       if (!driver || driver.category !== category) {
         return reply.code(400).send({ error: `invalid driver for ${category}: ${driverId}` });
       }
+
+      const id = randomUUID();
+      const fullConfig: Record<string, unknown> = { ...config };
+
+      let device;
       try {
-        registry.create(driverId, config); // validates required fields
+        device = registry.create(driverId, config); // validates required fields
       } catch (err) {
         return reply.code(400).send({ error: (err as Error).message });
       }
+
+      // If the device supports input push, set it up now: generate Digest creds,
+      // configure the device to push to us, store the creds. Done before
+      // persisting so we don't store half-configured rows.
+      if (hasPushConfig(device)) {
+        const host = String(config.host ?? "");
+        const backendIp = backendIpForDevice(host);
+        if (!backendIp) {
+          return reply.code(400).send({
+            error: `cannot determine the backend IP on the device's subnet (${host}). Set BACKEND_HOST_IP.`,
+          });
+        }
+        const pushUser = "dingtian";
+        // 24 hex chars = 96 bits. The Dingtian `pass` field caps at 31 chars
+        // (longer is silently truncated → auth mismatch), so keep it short.
+        const pushPassword = randomBytes(12).toString("hex");
+        try {
+          await device.configureInputPush({
+            host: backendIp,
+            port: backendPort(),
+            pathBase: `/api/devices/${driverId}/${id}/input`,
+            auth: { user: pushUser, password: pushPassword },
+          });
+        } catch (err) {
+          return reply
+            .code(502)
+            .send({ error: `device push config failed: ${(err as Error).message}` });
+        }
+        fullConfig.pushUser = pushUser;
+        fullConfig.pushPassword = pushPassword;
+      }
+
       const row = {
-        id: randomUUID(),
+        id,
         lane,
         category,
         driverId,
-        config,
+        config: fullConfig,
         enabled: true,
       };
       await db.insert(laneDevices).values(row);
-      return reply.code(201).send(row);
+      // Don't echo the push secret back.
+      const { pushPassword: _omit, ...safeConfig } = fullConfig;
+      return reply.code(201).send({ ...row, config: safeConfig });
     },
   );
 

apps/server/src/server.ts

@@ -44,8 +44,10 @@ export async function buildServer(opts: BuildOptions = {}): Promise<FastifyInsta
   // catalog at first-run. See wiki/concepts/first-run-setup.md.
   await setupRoutes(app, db);
 
-  // Inbound device pushes (e.g. Dingtian Input Link URL → button events).
-  await deviceRoutes(app);
+  // Inbound device pushes (e.g. Dingtian Input Link URL → button events),
+  // guarded by source-IP allowlist + a shared-secret path token, both read from
+  // the device's lane_devices config (written on assign).
+  await deviceRoutes(app, db);
 
   // TODO: entry flow (input event → signed event → print → relay), event-log routes.