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");
+}