feat(ap4): defend forwarded identity headers

.env.example

@@ -11,6 +11,7 @@ TOKEN_MEDIATING_CLIENT_SECRET=change-me-token-mediating-client-secret
 BFF_CLIENT_SECRET=change-me-bff-client-secret
 EDGE_PROXY_CLIENT_SECRET=change-me-edge-proxy-client-secret
 OAUTH2_PROXY_COOKIE_SECRET=generate-a-base64-encoded-32-byte-secret
+INTERNAL_AUTH_TOKEN=generate-a-long-random-edge-to-backend-token
 ADMIN_USER_PASSWORD=change-me-admin-user-password
 REGULAR_USER_PASSWORD=change-me-regular-user-password
 

README.md

@@ -107,8 +107,11 @@ gitignored `build/keycloak-export/`에 권한 `0600`으로만 저장됩니다.
 ```
 
 첫 feature에서는 oauth2-proxy를 `http://localhost:4180`에 직접 노출해
-OIDC redirect/PKCE/callback과 forwarded-user를 분리 확인합니다. 최종
-구성은 `http://localhost:8088` Nginx를 단일 진입점으로 사용합니다.
+OIDC redirect/PKCE/callback과 forwarded-user를 분리 확인합니다. 두 번째
+feature부터 `http://localhost:8088` Nginx가 단일 진입점이며, 내부
+`auth_request`는 브라우저 요청을 login 302로, API 요청을 JSON 401로
+구분합니다. 최종 feature에서는 backend와 oauth2-proxy의 호스트 노출을
+제거하고 Nginx 헤더 덮어쓰기와 내부 토큰 검증으로 spoofing을 막습니다.
 자세한 내용은
 [`docs/ap4-edge-forward-auth.md`](docs/ap4-edge-forward-auth.md)를
 참고하세요.

backend/src/main/java/com/example/keycloakpattern/EdgeIdentityController.java

@@ -1,44 +1,56 @@
 package com.example.keycloakpattern;
 
+import java.nio.charset.StandardCharsets;
+import java.security.MessageDigest;
 import java.util.LinkedHashMap;
 import java.util.Map;
 
 import jakarta.servlet.http.HttpServletRequest;
 
 import org.springframework.http.ResponseEntity;
+import org.springframework.beans.factory.annotation.Value;
 import org.springframework.web.bind.annotation.GetMapping;
 import org.springframework.web.bind.annotation.RestController;
 
 @RestController
 public class EdgeIdentityController {
 
+    private final byte[] internalAuthToken;
+
+    EdgeIdentityController(@Value("${edge.internal-auth-token}") String internalAuthToken) {
+        if (!hasText(internalAuthToken)) {
+            throw new IllegalStateException("edge.internal-auth-token must be configured");
+        }
+        this.internalAuthToken = internalAuthToken.getBytes(StandardCharsets.UTF_8);
+    }
+
     @GetMapping("/edge/me")
     ResponseEntity<Map<String, Object>> currentUser(HttpServletRequest request) {
         String authRequestUser = request.getHeader("X-Auth-Request-User");
-        String forwardedUser = request.getHeader("X-Forwarded-User");
-        String user = hasText(authRequestUser) ? authRequestUser : forwardedUser;
-        if (!hasText(user)) {
+        if (!hasText(authRequestUser) || !hasValidInternalToken(request)) {
             return ResponseEntity.status(401).body(Map.of(
                 "error",
-                "trusted edge identity header is required"
+                "trusted edge authentication is required"
             ));
         }
 
         Map<String, Object> response = new LinkedHashMap<>();
         response.put("pattern", "AP4-edge-forward-auth");
-        response.put("user", user);
-        response.put("email", firstNonBlank(
-            request.getHeader("X-Auth-Request-Email"),
-            request.getHeader("X-Forwarded-Email")
-        ));
-        response.put("identityHeader", hasText(authRequestUser)
-            ? "X-Auth-Request-User"
-            : "X-Forwarded-User");
+        response.put("user", authRequestUser);
+        response.put("email", request.getHeader("X-Auth-Request-Email"));
+        response.put("identityHeader", "X-Auth-Request-User");
         return ResponseEntity.ok(response);
     }
 
-    private static String firstNonBlank(String first, String second) {
-        return hasText(first) ? first : second;
+    private boolean hasValidInternalToken(HttpServletRequest request) {
+        String suppliedToken = request.getHeader("X-Internal-Auth-Token");
+        if (!hasText(suppliedToken)) {
+            return false;
+        }
+        return MessageDigest.isEqual(
+            internalAuthToken,
+            suppliedToken.getBytes(StandardCharsets.UTF_8)
+        );
     }
 
     private static boolean hasText(String value) {

backend/src/main/resources/application.yml

@@ -1,6 +1,9 @@
 server:
   port: ${SERVER_PORT:8081}
 
+edge:
+  internal-auth-token: ${EDGE_INTERNAL_AUTH_TOKEN:}
+
 spring:
   application:
     name: keycloak-pattern-api

backend/src/test/java/com/example/keycloakpattern/ApiSecurityTest.java

@@ -11,7 +11,7 @@ import org.springframework.boot.test.autoconfigure.web.servlet.AutoConfigureMock
 import org.springframework.boot.test.context.SpringBootTest;
 import org.springframework.test.web.servlet.MockMvc;
 
-@SpringBootTest
+@SpringBootTest(properties = "edge.internal-auth-token=test-internal-edge-token")
 @AutoConfigureMockMvc
 class ApiSecurityTest {
 
@@ -42,18 +42,34 @@ class ApiSecurityTest {
     }
 
     @Test
-    void edgeEndpointRejectsMissingIdentityHeader() throws Exception {
+    void edgeEndpointRejectsMissingTrustedHeaders() throws Exception {
         mockMvc.perform(get("/edge/me"))
             .andExpect(status().isUnauthorized());
     }
 
     @Test
-    void edgeEndpointCurrentlyTrustsForwardedUserHeader() throws Exception {
+    void edgeEndpointRejectsForgedIdentityWithoutInternalToken() throws Exception {
         mockMvc.perform(get("/edge/me")
-                .header("X-Forwarded-User", "regular-user")
-                .header("X-Forwarded-Email", "regular-user@example.test"))
+                .header("X-Auth-Request-User", "spoofed-admin"))
+            .andExpect(status().isUnauthorized());
+    }
+
+    @Test
+    void edgeEndpointRejectsWrongInternalToken() throws Exception {
+        mockMvc.perform(get("/edge/me")
+                .header("X-Auth-Request-User", "spoofed-admin")
+                .header("X-Internal-Auth-Token", "wrong-token"))
+            .andExpect(status().isUnauthorized());
+    }
+
+    @Test
+    void edgeEndpointAcceptsIdentityFromTrustedEdge() throws Exception {
+        mockMvc.perform(get("/edge/me")
+                .header("X-Auth-Request-User", "regular-user")
+                .header("X-Auth-Request-Email", "regular-user@example.test")
+                .header("X-Internal-Auth-Token", "test-internal-edge-token"))
             .andExpect(status().isOk())
             .andExpect(jsonPath("$.user").value("regular-user"))
-            .andExpect(jsonPath("$.identityHeader").value("X-Forwarded-User"));
+            .andExpect(jsonPath("$.identityHeader").value("X-Auth-Request-User"));
     }
 }

docker-compose.yml

@@ -69,8 +69,9 @@ services:
       SERVER_PORT: "8081"
       SPRING_SECURITY_OAUTH2_RESOURCESERVER_JWT_ISSUER_URI: http://localhost:8080/realms/keycloak-patterns
       SPRING_SECURITY_OAUTH2_RESOURCESERVER_JWT_JWK_SET_URI: http://keycloak:8080/realms/keycloak-patterns/protocol/openid-connect/certs
-    ports:
-      - "127.0.0.1:8081:8081"
+      EDGE_INTERNAL_AUTH_TOKEN: ${INTERNAL_AUTH_TOKEN:?set INTERNAL_AUTH_TOKEN in .env}
+    expose:
+      - "8081"
     depends_on:
       keycloak:
         condition: service_healthy
@@ -98,11 +99,13 @@ services:
       - --oidc-jwks-url=http://keycloak:8080/realms/keycloak-patterns/protocol/openid-connect/certs
       - --profile-url=http://keycloak:8080/realms/keycloak-patterns/protocol/openid-connect/userinfo
       - --validate-url=http://keycloak:8080/realms/keycloak-patterns/protocol/openid-connect/userinfo
-      - --redirect-url=http://localhost:4180/oauth2/callback
+      - --redirect-url=http://localhost:8088/oauth2/callback
       - --upstream=http://app:8081
       - --email-domain=*
       - --scope=openid profile email
       - --code-challenge-method=S256
+      - --reverse-proxy=true
+      - --trusted-proxy-ip=172.30.40.10/32
       - --cookie-name=AP4_SESSION
       - --cookie-secure=false
       - --cookie-samesite=lax
@@ -110,14 +113,14 @@ services:
       - --skip-provider-button=true
       - --set-xauthrequest=true
       - --pass-user-headers=true
-      - --whitelist-domain=localhost:4180
+      - --whitelist-domain=localhost:8088
       - --whitelist-domain=localhost:8080
     environment:
       OAUTH2_PROXY_CLIENT_ID: edge-proxy
       OAUTH2_PROXY_CLIENT_SECRET: ${EDGE_PROXY_CLIENT_SECRET:?set EDGE_PROXY_CLIENT_SECRET in .env}
       OAUTH2_PROXY_COOKIE_SECRET: ${OAUTH2_PROXY_COOKIE_SECRET:?set OAUTH2_PROXY_COOKIE_SECRET in .env}
-    ports:
-      - "127.0.0.1:4180:4180"
+    expose:
+      - "4180"
     depends_on:
       keycloak:
         condition: service_healthy
@@ -139,10 +142,12 @@ services:
   nginx:
     build:
       context: ./frontend
+    environment:
+      INTERNAL_AUTH_TOKEN: ${INTERNAL_AUTH_TOKEN:?set INTERNAL_AUTH_TOKEN in .env}
     ports:
       - "127.0.0.1:${NGINX_PORT:-8088}:80"
     depends_on:
-      app:
+      oauth2-proxy:
         condition: service_healthy
     healthcheck:
       test:
@@ -152,7 +157,8 @@ services:
       timeout: 5s
       retries: 12
     networks:
-      - keycloak-net
+      keycloak-net:
+        ipv4_address: 172.30.40.10
     restart: unless-stopped
 
 volumes:
@@ -162,3 +168,6 @@ volumes:
 networks:
   keycloak-net:
     driver: bridge
+    ipam:
+      config:
+        - subnet: 172.30.40.0/24

docs/ap4-edge-forward-auth.md

@@ -29,3 +29,42 @@ loopback에 publish되어 있습니다. 따라서 로컬에서 직접
 `X-Forwarded-User: spoofed-admin`을 보내면 우회가 재현됩니다. 이후
 Nginx `auth_request` 통합을 거쳐 최종 feature에서 backend no-publish와
 내부 shared-secret 검증을 함께 적용합니다.
+
+## 두 번째 단계: Nginx `auth_request`
+
+`feature/keycloak-nginx-auth-request-integration`부터 외부 진입점은
+`http://localhost:8088` Nginx 하나입니다. oauth2-proxy의 4180 포트는
+Compose 네트워크에만 expose됩니다.
+
+- Nginx의 정확 일치 `location = /oauth2/auth`는 `internal`이라 외부에서
+  직접 호출할 수 없습니다.
+- 인증 서브리퀘스트에는 본문을 보내지 않고 `Content-Length`도
+  비웁니다.
+- 일반 브라우저 요청의 401은 `/oauth2/start` 302로 변환합니다.
+- API 요청 `/api/edge`는 redirect하지 않고 JSON 401을 반환합니다.
+- 인증 성공 시 oauth2-proxy의 `X-Auth-Request-User`와 email만 backend로
+  전달합니다.
+
+Nginx 컨테이너 IP를 전용 Compose subnet에서 고정하고 oauth2-proxy의
+trusted proxy를 그 단일 IP로 제한합니다. 다만 이 단계에서는 backend
+8081이 로컬 호스트에 열려 있어 신뢰 헤더를 직접 위조할 수 있습니다.
+그 재현 조건은 마지막 feature에서 제거합니다.
+
+## 마지막 단계: 신뢰 경계와 헤더 스푸핑 방어
+
+`feature/keycloak-header-spoofing-defense`에서는 신뢰 경계를 실제
+네트워크와 application 양쪽에서 강제합니다.
+
+1. backend 8081과 oauth2-proxy 4180은 host에 publish하지 않습니다.
+   브라우저가 접근 가능한 application 포트는 Nginx 8088뿐입니다.
+2. Nginx는 client가 보낸 `X-Auth-Request-User`, email, 내부 토큰을
+   그대로 전달하지 않고 oauth2-proxy 결과와 server-side 토큰으로
+   항상 덮어씁니다.
+3. backend는 `X-Auth-Request-User`와 `X-Internal-Auth-Token`이 모두
+   유효할 때만 edge identity를 받아들이며 token은 constant-time으로
+   비교합니다.
+
+shared token은 방어 심층화 수단입니다. 운영에서는 Secret Manager나
+orchestrator secret으로 주입하고 주기적으로 교체해야 합니다. 서비스
+간 mTLS 또는 service mesh identity를 사용할 수 있다면 단순 shared
+token보다 강한 workload identity로 대체하는 편이 좋습니다.

e2e/pattern4.mjs

@@ -4,6 +4,9 @@ import { chromium } from "playwright-core";
 const password = process.env.E2E_PASSWORD;
 assert.ok(password, "E2E_PASSWORD must be set");
 
+const edgeBaseUrl = "http://localhost:8088";
+const edgeEntryUrl = `${edgeBaseUrl}/`;
+
 async function completeKeycloakLogin(page) {
   for (let attempt = 1; attempt <= 2; attempt += 1) {
     await page.locator("#username").fill(
@@ -13,11 +16,11 @@ async function completeKeycloakLogin(page) {
     await page.locator("#kc-login").click();
     await page.waitForLoadState("domcontentloaded");
 
-    if (page.url() === "http://localhost:4180/edge/me") {
+    if (page.url() === edgeEntryUrl) {
       return;
     }
     if (attempt === 1) {
-      await page.goto("http://localhost:4180/oauth2/start?rd=%2Fedge%2Fme");
+      await page.goto(`${edgeBaseUrl}/oauth2/start?rd=${encodeURIComponent(edgeEntryUrl)}`);
       await page.waitForURL(/localhost:8080/u);
     }
   }
@@ -40,7 +43,7 @@ try {
 
   const edgeResponsePromise = page.waitForResponse(
     (response) =>
-      response.url() === "http://localhost:4180/edge/me" &&
+      response.url() === edgeEntryUrl &&
       response.status() === 302,
   );
   const authorizationRequestPromise = page.waitForRequest((request) =>
@@ -48,7 +51,7 @@ try {
       "/protocol/openid-connect/auth?approval_prompt=",
     ),
   );
-  await page.goto("http://localhost:4180/edge/me");
+  await page.goto(edgeEntryUrl);
   const unauthenticatedEdgeResponse = await edgeResponsePromise;
   assert.equal(unauthenticatedEdgeResponse.status(), 302);
 
@@ -63,10 +66,10 @@ try {
   const edgeIdentity = JSON.parse(await page.locator("body").innerText());
   assert.equal(edgeIdentity.pattern, "AP4-edge-forward-auth");
   assert.ok(edgeIdentity.user);
-  assert.equal(edgeIdentity.identityHeader, "X-Forwarded-User");
+  assert.equal(edgeIdentity.identityHeader, "X-Auth-Request-User");
 
   const callbackRequest = browserRequests.find(({ url }) =>
-    url.startsWith("http://localhost:4180/oauth2/callback?"),
+    url.startsWith(`${edgeBaseUrl}/oauth2/callback?`),
   );
   assert.ok(callbackRequest);
   assert.equal(callbackRequest.method, "GET");
@@ -78,7 +81,7 @@ try {
     "the confidential token exchange must be server-to-server",
   );
 
-  const cookies = await context.cookies("http://localhost:4180/");
+  const cookies = await context.cookies(edgeEntryUrl);
   const sessionCookie = cookies.find((cookie) => cookie.name === "AP4_SESSION");
   assert.ok(sessionCookie);
   assert.equal(sessionCookie.httpOnly, true);
@@ -94,17 +97,41 @@ try {
   assert.deepEqual(storage.sessionStorage, []);
   assert.equal(storage.readableCookies.includes("AP4_SESSION"), false);
 
-  const missingHeader = await fetch("http://localhost:8081/edge/me");
-  assert.equal(missingHeader.status, 401);
-  const directSpoof = await fetch("http://localhost:8081/edge/me", {
-    headers: { "X-Forwarded-User": "spoofed-admin" },
+  const spoofAttempt = await page.evaluate(async () => {
+    const response = await fetch("/", {
+      headers: {
+        "X-Auth-Request-User": "spoofed-admin",
+        "X-Auth-Request-Email": "spoofed-admin@example.test",
+        "X-Internal-Auth-Token": "attacker-controlled-token",
+      },
+    });
+    return { status: response.status, body: await response.json() };
   });
-  assert.equal(directSpoof.status, 200);
-  const spoofedIdentity = await directSpoof.json();
-  assert.equal(spoofedIdentity.user, "spoofed-admin");
+  assert.equal(spoofAttempt.status, 200);
+  assert.equal(spoofAttempt.body.user, edgeIdentity.user);
+  assert.notEqual(spoofAttempt.body.user, "spoofed-admin");
+
+  const externalAuthSubrequest = await fetch(`${edgeBaseUrl}/oauth2/auth`);
+  assert.equal(externalAuthSubrequest.status, 404);
+
+  const apiResponse = await fetch(`${edgeBaseUrl}/api/edge`, {
+    redirect: "manual",
+  });
+  assert.equal(apiResponse.status, 401);
+  assert.equal(apiResponse.headers.get("location"), null);
+
+  await assert.rejects(
+    fetch("http://localhost:4180/ping"),
+    "oauth2-proxy must not be published on the host",
+  );
+
+  await assert.rejects(
+    fetch("http://localhost:8081/edge/me"),
+    "backend must not be published on the host",
+  );
 
   console.log(
-    "pattern4 oauth2-proxy verified: redirect, PKCE login, forwarded-user 200, direct spoof precondition",
+    "pattern4 hardened edge verified: auth_request, no backend publish, spoofed headers overwritten",
   );
 } finally {
   await browser.close();

frontend/Dockerfile

@@ -1,4 +1,4 @@
 FROM nginx:1.29-alpine
 
-COPY nginx.conf /etc/nginx/conf.d/default.conf
+COPY default.conf.template /etc/nginx/templates/default.conf.template
 COPY index.html /usr/share/nginx/html/index.html

frontend/default.conf.template

@@ -0,0 +1,75 @@
+server {
+    listen 80;
+    server_name _;
+
+    large_client_header_buffers 4 16k;
+
+    location = /health {
+        access_log off;
+        default_type text/plain;
+        return 200 "ok\n";
+    }
+
+    location = /oauth2/auth {
+        internal;
+        proxy_pass http://oauth2-proxy:4180;
+        proxy_pass_request_body off;
+        proxy_set_header Content-Length "";
+        proxy_set_header X-Original-URL $scheme://$http_host$request_uri;
+        proxy_set_header X-Real-IP $remote_addr;
+        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
+        proxy_set_header X-Forwarded-Host $http_host;
+        proxy_set_header X-Forwarded-Proto $scheme;
+        proxy_set_header X-Forwarded-Uri $request_uri;
+    }
+
+    location /oauth2/ {
+        proxy_pass http://oauth2-proxy:4180;
+        proxy_http_version 1.1;
+        proxy_set_header Host $http_host;
+        proxy_set_header X-Real-IP $remote_addr;
+        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
+        proxy_set_header X-Forwarded-Host $http_host;
+        proxy_set_header X-Forwarded-Proto $scheme;
+        proxy_set_header X-Auth-Request-Redirect $scheme://$http_host$request_uri;
+    }
+
+    location = /api/edge {
+        auth_request /oauth2/auth;
+        error_page 401 = @api_unauthorized;
+
+        auth_request_set $auth_user $upstream_http_x_auth_request_user;
+        auth_request_set $auth_email $upstream_http_x_auth_request_email;
+        auth_request_set $auth_cookie $upstream_http_set_cookie;
+        add_header Set-Cookie $auth_cookie always;
+
+        proxy_pass http://app:8081/edge/me;
+        proxy_set_header X-Auth-Request-User $auth_user;
+        proxy_set_header X-Auth-Request-Email $auth_email;
+        proxy_set_header X-Internal-Auth-Token "${INTERNAL_AUTH_TOKEN}";
+    }
+
+    location / {
+        auth_request /oauth2/auth;
+        error_page 401 = @oauth2_signin;
+
+        auth_request_set $auth_user $upstream_http_x_auth_request_user;
+        auth_request_set $auth_email $upstream_http_x_auth_request_email;
+        auth_request_set $auth_cookie $upstream_http_set_cookie;
+        add_header Set-Cookie $auth_cookie always;
+
+        proxy_pass http://app:8081/edge/me;
+        proxy_set_header X-Auth-Request-User $auth_user;
+        proxy_set_header X-Auth-Request-Email $auth_email;
+        proxy_set_header X-Internal-Auth-Token "${INTERNAL_AUTH_TOKEN}";
+    }
+
+    location @oauth2_signin {
+        return 302 $scheme://$http_host/oauth2/start?rd=$scheme://$http_host$request_uri;
+    }
+
+    location @api_unauthorized {
+        default_type application/json;
+        return 401 '{"error":"authentication required"}';
+    }
+}

frontend/nginx.conf

@@ -1,26 +0,0 @@
-server {
-    listen 80;
-    server_name _;
-
-    root /usr/share/nginx/html;
-    index index.html;
-
-    location = /health {
-        access_log off;
-        default_type text/plain;
-        return 200 "ok\n";
-    }
-
-    location /api/ {
-        proxy_pass http://app:8081;
-        proxy_http_version 1.1;
-        proxy_set_header Host $host;
-        proxy_set_header X-Real-IP $remote_addr;
-        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
-        proxy_set_header X-Forwarded-Proto $scheme;
-    }
-
-    location / {
-        try_files $uri $uri/ /index.html;
-    }
-}

keycloak/import/keycloak-patterns-realm.json

@@ -116,7 +116,7 @@
       "serviceAccountsEnabled": false,
       "frontchannelLogout": true,
       "redirectUris": [
-        "http://localhost:4180/oauth2/callback"
+        "http://localhost:8088/oauth2/callback"
       ],
       "webOrigins": [],
       "attributes": {

scripts/verify-pattern4.sh

@@ -13,9 +13,29 @@ set +a
 docker compose down --volumes --remove-orphans
 docker compose up --build -d --wait
 
+docker compose exec -T nginx nginx -V 2>&1 |
+  grep -q -- '--with-http_auth_request_module'
+docker compose exec -T nginx nginx -T 2>&1 |
+  grep -q 'proxy_pass_request_body off'
+
+app_container_id="$(docker compose ps -q app)"
+published_app_port="$(docker inspect "$app_container_id" \
+  --format '{{with (index .NetworkSettings.Ports "8081/tcp")}}{{json .}}{{end}}')"
+if [ -n "$published_app_port" ]; then
+  echo "backend port 8081 must not be published on the host" >&2
+  exit 1
+fi
+
+if docker compose exec -T nginx wget -q -O /dev/null \
+  --header 'X-Auth-Request-User: spoofed-admin' \
+  http://app:8081/edge/me 2>/dev/null; then
+  echo "backend accepted a forged identity without the internal token" >&2
+  exit 1
+fi
+
 npm --prefix e2e ci
 E2E_USERNAME=regular-user \
 E2E_PASSWORD="$REGULAR_USER_PASSWORD" \
   npm --prefix e2e run test:pattern4
 
-echo "AP4 oauth2-proxy edge flow verified"
+echo "AP4 hardened Nginx auth_request edge flow verified"