From 4f93a5c92a794dc0c9835655b72e1f11c14daf9b Mon Sep 17 00:00:00 2001
From: donghyeon-ka <ehdgus6435@kumoh.ac.kr>
Date: Sat, 25 Jul 2026 16:50:52 +0900
Subject: [PATCH] feat: add validated Traefik ForwardAuth alternative

---
 deploy/traefik/dynamic.yml                   | 35 ++++++++++++++++++++
 deploy/traefik/traefik.yml                   | 14 ++++++++
 docs/traefik-forwardauth-alternative.md      | 22 ++++++++++++
 scripts/verify-traefik-forwardauth-config.sh | 28 ++++++++++++++++
 4 files changed, 99 insertions(+)
 create mode 100644 deploy/traefik/dynamic.yml
 create mode 100644 deploy/traefik/traefik.yml
 create mode 100644 docs/traefik-forwardauth-alternative.md
 create mode 100755 scripts/verify-traefik-forwardauth-config.sh

diff --git a/deploy/traefik/dynamic.yml b/deploy/traefik/dynamic.yml
new file mode 100644
index 0000000..b8fa627
--- /dev/null
+++ b/deploy/traefik/dynamic.yml
@@ -0,0 +1,35 @@
+http:
+  routers:
+    oauth:
+      entryPoints:
+        - web
+      rule: PathPrefix(`/oauth2/`)
+      service: oauth2-proxy
+      priority: 100
+    application:
+      entryPoints:
+        - web
+      rule: PathPrefix(`/`)
+      middlewares:
+        - keycloak-forward-auth
+      service: application
+
+  middlewares:
+    keycloak-forward-auth:
+      forwardAuth:
+        address: http://oauth2-proxy:4180/oauth2/auth
+        trustForwardHeader: false
+        authResponseHeaders:
+          - X-Auth-Request-User
+          - X-Auth-Request-Email
+          - Set-Cookie
+
+  services:
+    oauth2-proxy:
+      loadBalancer:
+        servers:
+          - url: http://oauth2-proxy:4180
+    application:
+      loadBalancer:
+        servers:
+          - url: http://app:8081
diff --git a/deploy/traefik/traefik.yml b/deploy/traefik/traefik.yml
new file mode 100644
index 0000000..538a423
--- /dev/null
+++ b/deploy/traefik/traefik.yml
@@ -0,0 +1,14 @@
+entryPoints:
+  web:
+    address: ":8080"
+
+providers:
+  file:
+    filename: /etc/traefik/dynamic.yml
+    watch: false
+
+api:
+  dashboard: false
+
+log:
+  level: INFO
diff --git a/docs/traefik-forwardauth-alternative.md b/docs/traefik-forwardauth-alternative.md
new file mode 100644
index 0000000..55d9003
--- /dev/null
+++ b/docs/traefik-forwardauth-alternative.md
@@ -0,0 +1,22 @@
+# Traefik ForwardAuth alternative
+
+Traefik의 `forwardAuth` middleware는 nginx `auth_request`와 같은 정책 지점을
+제공한다. 예제는 `/oauth2/auth`를 oauth2-proxy에 위임하고 성공 응답의
+허용된 identity headers만 application request로 복사한다.
+
+중요한 차이:
+
+- ForwardAuth 자체는 OIDC client나 session manager가 아니다. 이 예제에서도
+  oauth2-proxy가 code 교환과 cookie를 담당한다.
+- `trustForwardHeader=false`로 외부 forwarded header를 신뢰하지 않는다.
+- `/oauth2/` router는 callback/start 경로를 oauth2-proxy에 연결해야 한다.
+- nginx의 `error_page 401 -> /oauth2/start`와 같은 로그인 redirect UX는
+  Traefik errors middleware 또는 oauth2-proxy의 forward-auth redirect
+  profile을 추가로 설계해야 한다.
+- Docker socket label discovery 대신 file provider를 사용해 socket 노출을
+  피했다. Kubernetes에서는 Middleware/IngressRoute CRD라는 vendor-specific
+  운영 객체가 추가된다.
+
+이 repository의 실제 AP4 baseline은 학습 가시성이 높은 nginx 조합을
+유지한다. `verify-traefik-forwardauth-config.sh`는 대안 파일을 Traefik
+binary로 로드하고 즉시 발생하는 provider/config 오류가 없는지 확인한다.
diff --git a/scripts/verify-traefik-forwardauth-config.sh b/scripts/verify-traefik-forwardauth-config.sh
new file mode 100755
index 0000000..a3b931e
--- /dev/null
+++ b/scripts/verify-traefik-forwardauth-config.sh
@@ -0,0 +1,28 @@
+#!/usr/bin/env sh
+set -eu
+
+config_dir="$PWD/deploy/traefik"
+output_file="$(mktemp)"
+cleanup() {
+  rm -f "$output_file"
+}
+trap cleanup EXIT
+
+status=0
+timeout 4 docker run --rm \
+  -v "$config_dir:/etc/traefik:ro" \
+  traefik:v3.5.3 \
+  --configFile=/etc/traefik/traefik.yml >"$output_file" 2>&1 || status=$?
+
+if [ "$status" -ne 0 ] && [ "$status" -ne 124 ]; then
+  cat "$output_file" >&2
+  exit "$status"
+fi
+if rg -qi 'error|failed' "$output_file"; then
+  cat "$output_file" >&2
+  exit 1
+fi
+
+grep -q 'trustForwardHeader: false' deploy/traefik/dynamic.yml
+grep -q 'X-Auth-Request-User' deploy/traefik/dynamic.yml
+echo "Traefik file provider and ForwardAuth configuration verified"