Why

When DeerFlow's bundled nginx runs behind another TLS-terminating reverse proxy (e.g. Pangolin/Traefik, Cloudflare, Caddy) — a common way to expose a self-hosted DeerFlow publicly over HTTPS — login silently fails. The user submits valid credentials and is bounced straight back to the login screen with no session established.

Root cause: every location block hardcodes proxy_set_header X-Forwarded-Proto $scheme. The front proxy terminates TLS and reaches nginx over plain HTTP on the private hop, so $scheme is http, overwriting the https the front proxy already set. The Gateway then treats HTTPS browser traffic as HTTP, and:

• CSRFMiddleware.is_allowed_auth_origin computes the expected origin as http://<host>, which no longer matches the browser's Origin: https://<host>, so the login POST is rejected with 403 "Cross-site auth request denied" (backend/app/gateway/csrf_middleware.py).
• is_secure_request() returns false, so the access_token session cookie is set without Secure and without max-age (session-only).

What changed

nginx now preserves an upstream proxy's X-Forwarded-Proto instead of unconditionally overwriting it, via a map that falls back to $scheme when there is no upstream value:

map $http_x_forwarded_proto $forwarded_proto {
    default    $scheme;
    "~*^https" https;
}

All proxy_set_header X-Forwarded-Proto lines now use $forwarded_proto.

• Standalone make dev / Docker (nginx is the TLS edge): no incoming X-Forwarded-Proto → falls back to $scheme → behavior unchanged.
• Behind another HTTPS proxy: the real https scheme reaches the Gateway → the login origin check passes and session cookies regain Secure + max-age.

Note: this trusts an incoming X-Forwarded-Proto, which is the intended behavior when nginx sits behind a trusted front proxy. Operators who expose nginx's port directly to untrusted clients should terminate TLS at nginx (the $scheme fallback covers that) or restrict the trusted-proxy source.

Surface area

• Sandbox — docker/ or sandboxed execution (reverse-proxy config under docker/nginx/)
• Default behavior change (no — standalone deployments are byte-for-byte unchanged via the $scheme fallback)

Bug fix verification

nginx config is not exercised by the unit/E2E suites, so verified manually against the running stack (requests reaching the Gateway through nginx):

# BEFORE — X-Forwarded-Proto clobbered to http:
$ curl -s -o /dev/null -w '%{http_code}\n' -X POST http://localhost:2026/api/v1/auth/login/local \
    -H 'Host: example.com' -H 'Origin: https://example.com' \
    -H 'Content-Type: application/x-www-form-urlencoded' --data 'username=x@x.com&password=wrong'
403            # "Cross-site auth request denied"

# AFTER — front proxy's X-Forwarded-Proto: https preserved:
$ curl -s -o /dev/null -w '%{http_code}\n' -X POST http://localhost:2026/api/v1/auth/login/local \
    -H 'Host: example.com' -H 'X-Forwarded-Proto: https' -H 'Origin: https://example.com' \
    -H 'Content-Type: application/x-www-form-urlencoded' --data 'username=x@x.com&password=wrong'
401            # origin check passes → reaches credential check; access_token cookie now has `Secure`

The standalone case (no X-Forwarded-Proto) returns the same result as before via the $scheme fallback.

Validation

• nginx -t passes on the modified config.
• Manual reproduction above (403 → 401 flip; Secure flag restored on session cookies).
• No backend/frontend source touched; no frontend/ changes, so E2E is unaffected.

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