Force request host/scheme to App__Domain behind a proxy

The cookie login redirect and other absolute URLs are built from Request.Host;
behind a proxy that doesn't forward the Host header that's the internal IP:port,
so hitting the domain 302'd to the server IP. Rewrite scheme+host to App__Domain
on every request (after UseForwardedHeaders) so all generated URLs stay on the
public domain.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Core/Config/AppDomainOptions.cs

@@ -26,4 +26,11 @@ public class AppDomainOptions
 
         return domain + "/" + path.TrimStart('/');
     }
+
+    /// <summary>
+    /// The configured domain as an absolute base <see cref="Uri"/> (scheme + host [+ port]), or
+    /// <c>null</c> when no domain is set or it can't be parsed.
+    /// </summary>
+    public Uri? GetBaseUri() =>
+        BuildUrl("/") is { } url && Uri.TryCreate(url, UriKind.Absolute, out var uri) ? uri : null;
 }

Program.cs

@@ -309,6 +309,23 @@ var app = builder.Build();
 // Must run before anything that inspects the request scheme/IP (auth, OIDC, cookies).
 app.UseForwardedHeaders();
 
+// When App__Domain is set, rewrite every request's scheme + host to the public domain. The
+// framework builds absolute URLs (the cookie login redirect, the OIDC redirect_uri, …) from
+// Request.Scheme/Host; behind a proxy that doesn't forward the Host header these are the
+// internal host (server IP:port), so loading https://<domain>/ would 302 to http://<ip>:8080.
+// Forcing the host here keeps every generated URL on the public domain. Must run before auth.
+var publicBaseUri = appDomain.GetBaseUri();
+if (publicBaseUri is not null)
+{
+    var publicHost = HostString.FromUriComponent(publicBaseUri);
+    app.Use((context, next) =>
+    {
+        context.Request.Scheme = publicBaseUri.Scheme;
+        context.Request.Host   = publicHost;
+        return next(context);
+    });
+}
+
 // ── First-run bootstrap ───────────────────────────────────────────────────────
 // Seed a local admin when no users exist yet, so a plain-HTTP / LAN deployment that
 // can't use Microsoft OIDC (which requires HTTPS + a matching Entra redirect URI) can

README.md

@@ -46,6 +46,8 @@ These are separate and registered on **different** Entra apps. Don't conflate th
 
 > **HTTPS note.** The sign-in app is a confidential (Web) client, so Entra requires its `/signin-oidc` redirect URI to be **HTTPS** — plain HTTP is allowed only for `http://localhost`, not a LAN host/IP. To run OIDC on a plain-HTTP LAN deployment, put the app behind an HTTPS-terminating reverse proxy: register `https://your-host/signin-oidc`, and the app honours `X-Forwarded-Proto` (see `UseForwardedHeaders`) to build the correct `https` redirect. Without a proxy, OIDC sign-in won't work over a non-localhost HTTP host — use the local email/password login instead.
 
+> **Reverse-proxy host.** Set `App__Domain` so the app builds every redirect (cookie login, OIDC) against the public domain regardless of what host the proxy forwards. Without it, a proxy that doesn't forward the `Host` header makes the app 302 to the internal `IP:port` it actually received.
+
 Persistent state (profiles, settings, templates, logs, exports, certs) lives in `DataFolder`.
 
 ## Installation — Docker (prebuilt image)