Deploy on DigitalOcean App Platform (GitHub-source build) + consolidate audit-fixes

Deploy config:
- .do/app.yaml: build the Dockerfile directly from GitHub (deploy_on_push) instead
  of a pre-built DOCR image; NEXT_PUBLIC_* set RUN_AND_BUILD_TIME with the
  propertymanagement.network domain so they bake into the client bundle; add
  custom domains block (apex + www); wire Sentry DSN (server + browser).

Included pending work from the audit-fixes branch:
- AI provider abstraction (OpenAI/Anthropic, admin-selectable; Anthropic default)
- Per-landlord e-signature (DocuSign OAuth + Dropbox Sign) + migration 0010
- Outbound webhooks / Zapier integration
- PayPal removal (Stripe-only billing)
- Storage hardening (fail-loud when Spaces unconfigured), security fixes

Verified: full production Docker build (same build-args as DO) passes clean.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

app/api/integrations/[provider]/callback/route.ts

@@ -1,37 +1,51 @@
 import { NextResponse } from "next/server"
+import { cookies } from "next/headers"
+import { getSessionUser } from "@/lib/session"
+import { getAccountContext } from "@/lib/account"
 import { getProvider, saveConnection, type Provider } from "@/lib/accounting"
-import { verifyState } from "@/lib/accounting/state"
+import { verifyState, OAUTH_NONCE_COOKIE } from "@/lib/accounting/state"
 
 // OAuth callback — exchanges the code for tokens and stores the connection.
 export async function GET(request: Request, { params }: { params: Promise<{ provider: string }> }) {
   const { provider: pid } = await params
   const prov = getProvider(pid)
-  const url = new URL(request.url)
   const settings = new URL("/settings/integrations", request.url)
 
+  // Always clear the one-shot nonce cookie on the way out.
+  const cookieStore = await cookies()
+  const nonceCookie = cookieStore.get(OAUTH_NONCE_COOKIE)?.value
+  const done = (params: Record<string, string>) => {
+    for (const [k, v] of Object.entries(params)) settings.searchParams.set(k, v)
+    const res = NextResponse.redirect(settings)
+    res.cookies.set(OAUTH_NONCE_COOKIE, "", { path: "/", maxAge: 0 })
+    return res
+  }
+
+  const url = new URL(request.url)
   const code = url.searchParams.get("code")
   const state = url.searchParams.get("state")
   const realmId = url.searchParams.get("realmId") // QuickBooks includes this
   const oauthError = url.searchParams.get("error")
 
-  if (oauthError || !prov) {
-    settings.searchParams.set("error", "connect_failed")
-    return NextResponse.redirect(settings)
-  }
+  if (oauthError || !prov) return done({ error: "connect_failed" })
 
   const st = state ? verifyState(state) : null
-  if (!code || !st || st.provider !== pid) {
-    settings.searchParams.set("error", "invalid_state")
-    return NextResponse.redirect(settings)
+  // CSRF: the state's nonce must match the cookie set at connect time, and the
+  // current session must be the same owner that initiated the connect.
+  if (!code || !st || st.provider !== pid || !nonceCookie || nonceCookie !== st.nonce) {
+    return done({ error: "invalid_state" })
   }
+  const user = await getSessionUser()
+  if (!user) return done({ error: "invalid_state" })
+  const ctx = await getAccountContext(user.id)
+  if (ctx.ownerId !== st.ownerId) return done({ error: "invalid_state" })
 
   try {
     const tokens = await prov.exchangeCode(code, realmId)
     if (!tokens.realmId) throw new Error("No organisation returned from provider")
     await saveConnection(st.ownerId, pid as Provider, tokens)
-    settings.searchParams.set("connected", pid)
+    return done({ connected: pid })
   } catch {
-    settings.searchParams.set("error", "connect_failed")
+    return done({ error: "connect_failed" })
   }
-  return NextResponse.redirect(settings)
 }

app/api/integrations/[provider]/connect/route.ts

@@ -1,8 +1,9 @@
+import crypto from "crypto"
 import { NextResponse } from "next/server"
 import { getSessionUser } from "@/lib/session"
 import { getAccountContext } from "@/lib/account"
 import { getProvider } from "@/lib/accounting"
-import { signState } from "@/lib/accounting/state"
+import { signState, OAUTH_NONCE_COOKIE } from "@/lib/accounting/state"
 
 // Starts the OAuth connect flow for an accounting provider (owner-only).
 export async function GET(request: Request, { params }: { params: Promise<{ provider: string }> }) {
@@ -28,6 +29,17 @@ export async function GET(request: Request, { params }: { params: Promise<{ prov
     return NextResponse.redirect(settings)
   }
 
-  const state = signState({ ownerId: ctx.ownerId, provider: pid })
-  return NextResponse.redirect(prov.getAuthUrl(state))
+  // Bind the OAuth round-trip to this browser: a random nonce goes into the
+  // signed state AND an httpOnly cookie; the callback requires them to match.
+  const nonce = crypto.randomUUID()
+  const state = signState({ ownerId: ctx.ownerId, provider: pid, nonce })
+  const res = NextResponse.redirect(prov.getAuthUrl(state))
+  res.cookies.set(OAUTH_NONCE_COOKIE, nonce, {
+    httpOnly: true,
+    secure: process.env.NODE_ENV === "production",
+    sameSite: "lax",
+    path: "/",
+    maxAge: 600,
+  })
+  return res
 }