fix(portal): add invitation links and correct customer login routing

backend/src/utils/loginTenant.ts

@@ -0,0 +1,33 @@
+import type { FastifyInstance } from "fastify"
+import { and, eq } from "drizzle-orm"
+import { authProfiles, authTenantUsers } from "../../db/schema"
+
+export async function resolveLoginTenant(server: FastifyInstance, userId: string, domainTenantId: number | null) {
+    const memberships = await server.db
+        .selectDistinct({
+            tenantId: authTenantUsers.tenant_id,
+            portalCustomerId: authProfiles.customer_for_portal,
+        })
+        .from(authTenantUsers)
+        .leftJoin(authProfiles, and(
+            eq(authProfiles.user_id, authTenantUsers.user_id),
+            eq(authProfiles.tenant_id, authTenantUsers.tenant_id),
+            eq(authProfiles.active, true)
+        ))
+        .where(eq(authTenantUsers.user_id, userId))
+
+    if (domainTenantId) {
+        if (!memberships.some((membership) => membership.tenantId === domainTenantId)) {
+            throw Object.assign(new Error("Not a member of this tenant"), { statusCode: 403 })
+        }
+        return domainTenantId
+    }
+
+    // Portal invitations assign one customer account. Load its profile immediately,
+    // even when the customer signs in through the shared FEDEO address.
+    if (memberships.length === 1 && memberships[0].portalCustomerId) {
+        return memberships[0].tenantId
+    }
+
+    return null
+}

backend/src/utils/portalUrl.ts

@@ -0,0 +1,29 @@
+type PortalUrlSettings = {
+    portalDomain?: string | null
+    publicUrl?: string
+    apiBaseUrl?: string
+}
+
+/** Use deployment configuration, never request headers, for links sent by email. */
+export function getPortalLoginUrl({ portalDomain, publicUrl, apiBaseUrl }: PortalUrlSettings) {
+    const domain = portalDomain?.trim()
+    const candidates = [
+        { value: domain ? (/^https?:\/\//i.test(domain) ? domain : `https://${domain}`) : undefined },
+        { value: publicUrl?.trim() },
+        { value: apiBaseUrl?.trim(), originOnly: true },
+    ]
+
+    for (const { value, originOnly } of candidates) {
+        if (!value) continue
+        try {
+            const url = new URL(value)
+            if (!["http:", "https:"].includes(url.protocol) || url.username || url.password) continue
+            url.pathname = `${originOnly ? "" : url.pathname.replace(/\/+$/, "")}/login`
+            url.search = ""
+            url.hash = ""
+            return url.toString()
+        } catch { /* Try the next configured address. */ }
+    }
+
+    throw new Error("Für die Portal-Einladung fehlt eine gültige öffentliche FEDEO-Adresse.")
+}