初始提交：DSH 多租户平台（dshs）

src/web/auth.ts

@@ -0,0 +1,73 @@
+/**
+ * Password hashing, session-token helpers, and cookie assembly.
+ *
+ * Uses `node:crypto` scrypt so the scaffold has zero native dependency beyond
+ * SQLite; production may swap in argon2id without changing call sites.
+ * @module dshs/web/auth
+ */
+
+import { createHash, randomBytes, scrypt, timingSafeEqual } from 'node:crypto'
+import { promisify } from 'node:util'
+
+const scryptAsync = promisify(scrypt) as (password: string, salt: Buffer, keylen: number) => Promise<Buffer>
+
+const KEY_LENGTH = 64
+
+/** Hash a password into a `scrypt$<salt>$<hash>` string. */
+export async function hashPassword(password: string): Promise<string> {
+  const salt = randomBytes(16)
+  const derived = await scryptAsync(password, salt, KEY_LENGTH)
+  return `scrypt$${salt.toString('hex')}$${derived.toString('hex')}`
+}
+
+/** Constant-time password verification against a stored `scrypt$...` string. */
+export async function verifyPassword(password: string, stored: string): Promise<boolean> {
+  const [scheme, saltHex, hashHex] = stored.split('$')
+  if (scheme !== 'scrypt' || saltHex === undefined || hashHex === undefined) return false
+  const expected = Buffer.from(hashHex, 'hex')
+  const derived = await scryptAsync(password, Buffer.from(saltHex, 'hex'), KEY_LENGTH)
+  return derived.length === expected.length && timingSafeEqual(derived, expected)
+}
+
+/** Generate a fresh opaque session token. */
+export function newSessionToken(): string {
+  return randomBytes(32).toString('base64url')
+}
+
+/** Hash a session token for storage; the DB never holds the raw token. */
+export function hashSessionToken(token: string): string {
+  return createHash('sha256').update(token).digest('hex')
+}
+
+/** Extract a named cookie value from a `Cookie` header. */
+export function parseCookie(header: string | undefined, name: string): string | undefined {
+  if (!header) return undefined
+  for (const part of header.split(';')) {
+    const idx = part.indexOf('=')
+    if (idx === -1) continue
+    if (part.slice(0, idx).trim() === name) return part.slice(idx + 1).trim()
+  }
+  return undefined
+}
+
+/** Build a `Set-Cookie` value for the session token.
+ *
+ * `SameSite=None` (with `Secure`) when behind HTTPS so the cookie survives the
+ * cross-subdomain hop `dsh.<domain>` → `<user>.dsh.<domain>`; `SameSite=Lax`
+ * otherwise. The subdomain auth check still validates cookie ↔ slug, so the
+ * looser SameSite does not widen who a session can reach.
+ */
+export function sessionCookie(token: string, maxAgeSeconds: number, secure: boolean, domain?: string): string {
+  const flags = ['sid=' + token, 'HttpOnly', secure ? 'SameSite=None' : 'SameSite=Lax', 'Path=/', `Max-Age=${maxAgeSeconds}`]
+  if (secure) flags.push('Secure')
+  if (domain !== undefined && domain !== '') flags.push(`Domain=${domain}`)
+  return flags.join('; ')
+}
+
+/** Build a `Set-Cookie` value that expires the session cookie. */
+export function clearSessionCookie(secure: boolean, domain?: string): string {
+  const flags = ['sid=', 'HttpOnly', secure ? 'SameSite=None' : 'SameSite=Lax', 'Path=/', 'Max-Age=0']
+  if (secure) flags.push('Secure')
+  if (domain !== undefined && domain !== '') flags.push(`Domain=${domain}`)
+  return flags.join('; ')
+}