Hand the front door to Entra, and keep the keys out of the build

Auth.js replaces GoTrue. The sign-in still goes to the same Entra tenant,
but nothing sits between the app and the identity provider any more — the
code exchange, state, nonce and the session cookie are ours.

lib/auth/session.ts stays the only place that knows where a user id comes
from, which is why this was one file and not fifty. What it returns is now
app_users.id. app_upsert_user() maps the Entra `oid` onto it, and for an
address that already has a profiles row it adopts that id instead of
minting a new one — otherwise everyone would have been signed in and cut
off from their own notes, drafts and audit trail at the same time.

That upsert is the one write that cannot have a session context yet: the
id is what it produces. It runs as a SECURITY DEFINER function that may
touch app_users and nothing else, which is a far smaller lever than the
service key that used to answer this class of problem.

The proxy no longer checks HR rights. It has no database connection, and
putting role/is_active in the token would have frozen the claim until the
next sign-in. The check moved to where it can read the current truth: the
app layout on every render, requireHrUser() for the export routes, and
underneath both, RLS.

Two things only came out by running it:

  - `export const proxy = auth(…)` is not a function declaration, so
    Next.js never found it and every request 404'd. `next build` reported
    success and listed the proxy. In the function config form auth() also
    returns the handler as a promise, so it needs an await. The proxy test
    now mocks it as a promise for that reason — a friendlier mock would
    let the same bug back in.

  - A missing AUTH_MICROSOFT_ENTRA_ID_ISSUER silently falls back to
    /common/, and the redirect really did go there. That would let any
    Microsoft account sign in, including a private one, and it would never
    look broken. It now refuses to start in production.

Neither build nor image needs credentials any more: the pool is created on
first use, the auth config is evaluated per request, and there are no
NEXT_PUBLIC_* values left to bake in. One image now runs in every
environment.

Verified: typecheck, lint, 187 tests, build, and by hand in the browser —
/employees redirects to /login, and the sign-in button reaches the Entra
page with PKCE and the callback URL that goes into the app registration.
Not verified against a real database; there is still no DATABASE_URL.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

auth.ts

@@ -0,0 +1,63 @@
+import "server-only";
+import NextAuth from "next-auth";
+import { authConfig } from "@/lib/auth/config";
+import { asSystem, sql } from "@/lib/db";
+
+// Die vollständige Anmeldung — die Fassung, die die Datenbank kennt.
+//
+// Aufgeteilt ist sie, weil proxy.ts nur den Teil aus lib/auth/config.ts lädt.
+// Hier kommt das dazu, was einmal pro Anmeldung passieren muss: aus der
+// Kennung, die Entra ausstellt, eine Kennung machen, die diese Anwendung
+// versteht.
+
+/**
+ * Legt die app_users-Zeile an oder frischt sie auf und liefert die Kennung,
+ * die überall sonst als `userId` durchgereicht wird.
+ *
+ * Die Datenbankfunktion ist SECURITY DEFINER und darf genau dieses eine:
+ * app_users schreiben. Für den einen Schreibvorgang, für den es noch keinen
+ * Sitzungskontext geben kann, ist das der kleinstmögliche Hebel — früher lag
+ * hier ein Dienstschlüssel, der jede Zeile jeder Tabelle lesen konnte.
+ */
+async function upsertAppUser(externalId: string, email: string, fullName: string | null): Promise<string> {
+  const row = await asSystem(async (tx) => {
+    const result = await sql<{ id: string }>`
+      select app_upsert_user(${externalId}, ${email}, ${fullName}) as id
+    `.execute(tx);
+    return result.rows[0];
+  });
+
+  if (!row?.id) throw new Error("app_upsert_user() lieferte keine Kennung.");
+  return row.id;
+}
+
+export const { handlers, auth, signIn, signOut } = NextAuth(() => ({
+  ...authConfig(),
+  callbacks: {
+    async jwt({ token, profile }) {
+      // `profile` liegt nur beim ersten Durchlauf nach der Rückkehr von Entra
+      // vor. Danach wird das Token nur noch weitergereicht — die Datenbank
+      // wird also einmal pro Anmeldung befragt, nicht einmal pro Aufruf.
+      if (!profile) return token;
+
+      const externalId = typeof profile.oid === "string" ? profile.oid : null;
+      const email = [profile.email, profile.preferred_username, profile.upn].find(
+        (v): v is string => typeof v === "string" && v.length > 0
+      );
+
+      // Lieber abbrechen als eine Sitzung ohne Kennung ausstellen: die käme
+      // als `null` bei withUser() an, und die Policies gäben dann konsequent
+      // nichts zurück — was sich als „die Anwendung ist leer" zeigt statt als
+      // Anmeldefehler.
+      if (!externalId || !email) throw new Error("Entra lieferte weder oid noch E-Mail-Adresse.");
+
+      token.uid = await upsertAppUser(externalId, email, typeof profile.name === "string" ? profile.name : null);
+      return token;
+    },
+
+    async session({ session, token }) {
+      if (token.uid) session.user.id = token.uid;
+      return session;
+    },
+  },
+}));