diff --git a/containers/106-auth-outpost.md b/containers/106-auth-outpost.md
index 04a2c12..035e805 100644
--- a/containers/106-auth-outpost.md
+++ b/containers/106-auth-outpost.md
@@ -30,6 +30,17 @@ Runs one container — `ghcr.io/goauthentik/proxy` — that opens an outbound we
 ## Caddy wiring
 [Caddy (121)](121-caddy.md) `(authentik)` snippet `reverse_proxy`/`forward_auth` → `http://192.168.8.6:9000` (was `192.168.8.180:9000` on LXC 124). Tracked in `dtoro/caddy-conf`.
 
+## `sso.hubris.network` — the callback domain (critical)
+Domain-level (`forward_domain`) providers redirect the browser to `{external_host}/outpost.goauthentik.io/callback` after login. On LXC 124 that `external_host` was `auth.hubris.network`, which resolved (LAN) to Caddy → the 124 outpost — same box, so it worked. Post-migration `auth.hubris.network` points to the **VPS core**, so the callback hit the wrong outpost → **400 / redirect-uri mismatch**.
+
+Fix: the LAN outpost gets its **own** domain.
+- DNS: `sso.hubris.network → 192.168.8.175` (Caddy). *(in dnsmasq today — must be carried into Technitium in DNS Phase 2.)*
+- Caddy: site `sso.hubris.network { tls dns ionos; reverse_proxy 192.168.8.6:9000 }` (in `caddy-conf`).
+- Authentik: `hubris-forward-auth` and `Provider for Torrent` have `external_host=https://sso.hubris.network`; their `redirect_uris` must match (`set_oauth_defaults()` regenerates them from `external_host` — changing `external_host` alone does NOT update them).
+- `Provider for Artifacto` is `forward_single` on its own domain, so it was unaffected.
+
+**Lesson:** when the IdP core and the forward-auth outpost live on different hosts, the outpost needs a dedicated domain distinct from the core's — and proxy-provider `redirect_uris` must be regenerated, not just `external_host`.
+
 ## Related
 - [124 — authentik](124-authentik.md) — old embedded-outpost host (now DNS-only)
 - [Caddy (121)](121-caddy.md) — forward-auth consumer
diff --git a/infrastructure/dns.md b/infrastructure/dns.md
index f5d5bb0..4e168fb 100644
--- a/infrastructure/dns.md
+++ b/infrastructure/dns.md
@@ -15,6 +15,7 @@ There is **no wildcard on the LAN side**. Every subdomain needs an explicit entr
 
 ```
 address=/auth.hubris.network/82.165.190.79   # → VPS, not Caddy (Authentik migrated 2026-05-31)
+address=/sso.hubris.network/192.168.8.175    # → Caddy → LAN forward-auth outpost (106); added 2026-06-01
 address=/git.hubris.network/192.168.8.175
 address=/media.hubris.network/192.168.8.175
 address=/paperless.hubris.network/192.168.8.175