fix: harden proxy auth and SSRF defenses

app/api/auth/stalwart-context/route.ts

@@ -0,0 +1,46 @@
+import { NextRequest, NextResponse } from 'next/server';
+import { logger } from '@/lib/logger';
+import { JmapAuthVerificationError, verifyJmapAuth } from '@/lib/auth/verify-jmap-auth';
+import { setStalwartAuthContext } from '@/lib/stalwart/auth-context';
+
+function getSlot(request: NextRequest, bodySlot: unknown): number {
+  if (typeof bodySlot === 'number' && bodySlot >= 0 && bodySlot <= 4) {
+    return bodySlot;
+  }
+
+  const raw = request.nextUrl.searchParams.get('slot');
+  if (raw === null) return 0;
+
+  const slot = parseInt(raw, 10);
+  return Number.isNaN(slot) || slot < 0 || slot > 4 ? 0 : slot;
+}
+
+export async function POST(request: NextRequest) {
+  try {
+    const { serverUrl, username, authHeader, slot: bodySlot } = await request.json();
+
+    if (!serverUrl || !username || !authHeader) {
+      return NextResponse.json({ error: 'Missing required fields' }, { status: 400 });
+    }
+
+    const slot = getSlot(request, bodySlot);
+    const normalizedServerUrl = await verifyJmapAuth(serverUrl, authHeader);
+
+    await setStalwartAuthContext(slot, {
+      serverUrl: normalizedServerUrl,
+      username,
+      authHeader,
+    });
+
+    return NextResponse.json({ ok: true });
+  } catch (error) {
+    if (error instanceof JmapAuthVerificationError) {
+      return NextResponse.json({ error: error.message }, { status: error.status });
+    }
+
+    logger.error('Failed to store Stalwart auth context', {
+      error: error instanceof Error ? error.message : 'Unknown error',
+    });
+    return NextResponse.json({ error: 'Internal server error' }, { status: 500 });
+  }
+}