feat(api): add SRS Cloudflare Worker with email digest, charts, and D1 integration

apps/api/src/links.ts

@@ -0,0 +1,79 @@
+/**
+ * One-tap email links: `GET /log?p=704&r=pass&d=2026-08-31&sig=<hmac>`.
+ * The sig is HMAC-SHA256 over `p|r|d` with LINK_KEY (WebCrypto, hex).
+ * Verification is constant-time; links older than 3 days are rejected.
+ */
+
+async function hmacKey(secret: string): Promise<CryptoKey> {
+  return crypto.subtle.importKey(
+    "raw",
+    new TextEncoder().encode(secret),
+    { name: "HMAC", hash: "SHA-256" },
+    false,
+    ["sign", "verify"],
+  );
+}
+
+export async function signLink(
+  key: string,
+  p: number,
+  r: string,
+  d: string,
+): Promise<string> {
+  const mac = await crypto.subtle.sign(
+    "HMAC",
+    await hmacKey(key),
+    new TextEncoder().encode(`${p}|${r}|${d}`),
+  );
+  return [...new Uint8Array(mac)].map((b) => b.toString(16).padStart(2, "0")).join("");
+}
+
+export async function verifyLink(
+  key: string,
+  p: number,
+  r: string,
+  d: string,
+  sig: string,
+): Promise<boolean> {
+  if (!/^[0-9a-f]{64}$/.test(sig)) return false;
+  const bytes = new Uint8Array(32);
+  for (let i = 0; i < 32; i++) bytes[i] = Number.parseInt(sig.slice(i * 2, i * 2 + 2), 16);
+  // crypto.subtle.verify is constant-time; never compare hex strings directly.
+  return crypto.subtle.verify(
+    "HMAC",
+    await hmacKey(key),
+    bytes,
+    new TextEncoder().encode(`${p}|${r}|${d}`),
+  );
+}
+
+/** Constant-time equality for webhook signatures and admin bearer keys. */
+export async function timingSafeEqual(a: string, b: string): Promise<boolean> {
+  // HMAC both sides with a random key: unequal-length inputs and content
+  // differences are equally invisible to timing.
+  const key = await crypto.subtle.generateKey({ name: "HMAC", hash: "SHA-256" }, false, [
+    "sign",
+  ]);
+  const enc = new TextEncoder();
+  const [ma, mb] = await Promise.all([
+    crypto.subtle.sign("HMAC", key, enc.encode(a)),
+    crypto.subtle.sign("HMAC", key, enc.encode(b)),
+  ]);
+  const va = new Uint8Array(ma);
+  const vb = new Uint8Array(mb);
+  let diff = 0;
+  for (let i = 0; i < va.length; i++) diff |= va[i]! ^ vb[i]!;
+  return diff === 0;
+}
+
+/** GitHub webhook `X-Hub-Signature-256: sha256=<hex>` verification. */
+export async function verifyWebhook(
+  secret: string,
+  body: ArrayBuffer,
+  header: string | null,
+): Promise<boolean> {
+  if (!header?.startsWith("sha256=")) return false;
+  const mac = await crypto.subtle.sign("HMAC", await hmacKey(secret), body);
+  const expected = [...new Uint8Array(mac)].map((b) => b.toString(16).padStart(2, "0")).join("");
+  return timingSafeEqual(header.slice(7), expected);
+}