---
id: ADR-0004
title: Route every tenant API through a same-origin gateway
status: active
date: 2026-08-20
supersedes: []
tags: [architecture, multi-tenant, api, routing, nginx]
---

# ADR-0004: Route every tenant API through a same-origin gateway

## Context

The production bundle embedded `api.dexarmarket.ru` and constructed unknown tenant
URLs as `https://{tenant}.api.dexarmarket.ru:445`. Bootstrap used a different
route (`/bootstrap` on the storefront origin), while auth had its own fixed API
base. A custom domain could therefore use three different backend origins.

Directly calling the backend port is not a safe fallback: production returned
`403` for both a bootstrap request carrying `Origin: https://gorbushka.market`
and the corresponding CORS preflight. Meanwhile an unmatched `/bootstrap` on
the storefront nginx server fell through to `index.html`, producing a misleading
HTTP 200 with HTML instead of bootstrap JSON.

## Decision

Every tenant frontend uses one API base derived at runtime from the browser
origin: `{origin}/backend`.

- Bootstrap loads from `{origin}/backend/bootstrap`.
- Auth receives the same base through the `AUTH_API_URL` provider.
- Legacy endpoints append their existing paths to the same base.
- Versioned `/api/...` endpoints retain the `/api` prefix when routed.
- nginx owns `/backend/`, removes that prefix when proxying, and forwards the
  original `Host`, `X-Forwarded-For`, and `X-Forwarded-Proto` headers upstream.

The frontend contains no tenant/domain allowlist and no production backend
hostname. Tenant selection remains a server-side responsibility based on the
verified forwarded host.

## Consequences

Browser traffic is same-origin, so custom domains do not require per-tenant CORS
configuration and one bundle works for every attached domain. Bootstrap, auth,
legacy routes, and versioned routes cannot silently drift to different hosts.

Every nginx tenant/catch-all configuration must include the `/backend/` gateway.
Deploy verification must check that `/backend/bootstrap` returns JSON rather
than accepting a generic HTTP 200 from the SPA fallback. The upstream must still
reject unknown hosts; the gateway preserves `Host` but does not authenticate a
tenant by itself.