fix(web): /login leitet angemeldete Benutzer aufs Dashboard (bzw. sicheres next)

Nur bei gueltiger Signatur und ohne ausstehenden Kennwortwechsel; next ueber
sanitizeNextPath, /login als Ziel -> Dashboard. Gesperrte Konten: API lehnt
ab, Oberflaeche loescht das Cookie serverseitig, keine Schleife.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

apps/web/src/middleware.test.ts

@@ -1,6 +1,7 @@
 // @vitest-environment node
-import { NextRequest } from 'next/server';
+
 import { SignJWT } from 'jose';
+import { NextRequest } from 'next/server';
 import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest';
 import { middleware } from './middleware';
 
@@ -67,7 +68,9 @@ describe('middleware — Desktop-Client-Cookie (260917-h2s)', () => {
   });
 
   it('Test 6 (quick-260918-gza): /login mit dv/dc/dos setzt zusaetzlich tessera_desktop_client', async () => {
-    const req = new NextRequest('http://localhost:3000/login?desktop=1&dv=1.2.0&dc=a6d1a64&dos=windows');
+    const req = new NextRequest(
+      'http://localhost:3000/login?desktop=1&dv=1.2.0&dc=a6d1a64&dos=windows',
+    );
     const res = await middleware(req);
     expect(res.cookies.get('tessera_desktop')?.value).toBe('1');
     expect(res.cookies.get('tessera_desktop_client')?.value).toBe('1.2.0|a6d1a64|windows');
@@ -98,15 +101,23 @@ describe('middleware — Desktop-Client-Cookie (260917-h2s)', () => {
     );
     expect((await middleware(spaceInOs)).cookies.get('tessera_desktop_client')).toBeUndefined();
 
-    const missingDv = new NextRequest('http://localhost:3000/login?desktop=1&dc=a6d1a64&dos=windows');
+    const missingDv = new NextRequest(
+      'http://localhost:3000/login?desktop=1&dc=a6d1a64&dos=windows',
+    );
     expect((await middleware(missingDv)).cookies.get('tessera_desktop_client')).toBeUndefined();
 
-    const emptyCommit = new NextRequest('http://localhost:3000/login?desktop=1&dv=1.2.0&dc=&dos=linux');
-    expect((await middleware(emptyCommit)).cookies.get('tessera_desktop_client')?.value).toBe('1.2.0||linux');
+    const emptyCommit = new NextRequest(
+      'http://localhost:3000/login?desktop=1&dv=1.2.0&dc=&dos=linux',
+    );
+    expect((await middleware(emptyCommit)).cookies.get('tessera_desktop_client')?.value).toBe(
+      '1.2.0||linux',
+    );
   });
 
   it('Test 9 (quick-260918-gza, Redirect-Pfad): /dashboard ohne Session setzt beide Cookies auf dem 307', async () => {
-    const req = new NextRequest('http://localhost:3000/dashboard?desktop=1&dv=1.2.0&dc=a6d1a64&dos=linux');
+    const req = new NextRequest(
+      'http://localhost:3000/dashboard?desktop=1&dv=1.2.0&dc=a6d1a64&dos=linux',
+    );
     const res = await middleware(req);
     expect(res.status).toBe(307);
     expect(res.headers.get('location')).toContain('/login');
@@ -114,3 +125,65 @@ describe('middleware — Desktop-Client-Cookie (260917-h2s)', () => {
     expect(res.cookies.get('tessera_desktop_client')?.value).toBe('1.2.0|a6d1a64|linux');
   });
 });
+
+describe('middleware — /login bei bestehender Anmeldung (quick-260930)', () => {
+  beforeEach(() => {
+    vi.stubEnv('JWT_SECRET', 'test-secret');
+  });
+
+  afterEach(() => {
+    vi.unstubAllEnvs();
+  });
+
+  async function token(claims: Record<string, unknown> = {}) {
+    return new SignJWT({ sub: 'u1', ...claims })
+      .setProtectedHeader({ alg: 'HS256' })
+      .setIssuedAt()
+      .setExpirationTime('5m')
+      .sign(new TextEncoder().encode('test-secret'));
+  }
+
+  function loginReq(url: string, session?: string) {
+    return new NextRequest(url, session ? { headers: { cookie: `session=${session}` } } : {});
+  }
+
+  it('angemeldet: /login leitet aufs Dashboard um', async () => {
+    const res = await middleware(loginReq('http://localhost:3000/login', await token()));
+    expect(res.status).toBe(307);
+    expect(new URL(res.headers.get('location') as string).pathname).toBe('/');
+  });
+
+  it('angemeldet mit sicherem next: dorthin', async () => {
+    const res = await middleware(
+      loginReq('http://localhost:3000/login?next=%2Fadmin%2Fusers', await token()),
+    );
+    expect(new URL(res.headers.get('location') as string).pathname).toBe('/admin/users');
+  });
+
+  it('angemeldet mit fremdem oder zirkulaerem next: Dashboard', async () => {
+    for (const next of ['https%3A%2F%2Fboese.example', '%2F%2Fboese.example', '%2Flogin']) {
+      const res = await middleware(
+        loginReq(`http://localhost:3000/login?next=${next}`, await token()),
+      );
+      const loc = new URL(res.headers.get('location') as string);
+      expect(loc.host).toBe('localhost:3000');
+      expect(loc.pathname).toBe('/');
+    }
+  });
+
+  it('ohne oder mit ungueltigem Cookie: Anmeldeseite wie bisher', async () => {
+    const ohne = await middleware(loginReq('http://localhost:3000/login'));
+    expect(ohne.headers.get('x-middleware-next')).toBe('1');
+    const kaputt = await middleware(
+      loginReq('http://localhost:3000/login', 'kein.gueltiges.token'),
+    );
+    expect(kaputt.headers.get('x-middleware-next')).toBe('1');
+  });
+
+  it('Kennwortwechsel ausstehend: keine Umleitung von /login', async () => {
+    const res = await middleware(
+      loginReq('http://localhost:3000/login', await token({ mustChangePassword: true })),
+    );
+    expect(res.headers.get('x-middleware-next')).toBe('1');
+  });
+});