feat(ap2): hand off access token only

.gitignore

@@ -4,6 +4,7 @@
 *.iml
 
 backend/target/
+token-mediator/target/
 **/node_modules/
 frontend/dist/
 build/

README.md

@@ -97,38 +97,21 @@ Keycloak을 잠시 중지하고 export한 뒤 자동으로 다시 올립니다.
 runtime export에는 실제 client secret과 credential hash가 포함될 수 있어
 gitignored `build/keycloak-export/`에 권한 `0600`으로만 저장됩니다.
 
-## AP1: SPA Direct + Resource Server
+## AP2: Token-Mediating Backend
 
-`develop-keycloak-pattern1`은 vanilla JavaScript SPA가 `spa-public` client로
-Authorization Code + PKCE S256 로그인을 수행하는 패턴입니다. access/refresh
-token은 명시적인 in-memory store에만 보관되므로 새로고침하면 사라집니다.
+`develop-keycloak-pattern2`의 Spring confidential client는
+`http://localhost:8082`에서 실행됩니다. 브라우저는 로그인 redirect와
+HttpOnly `AP2_SESSION`만 사용하고, authorization code 교환과
+access/refresh token 보관은 backend가 담당합니다.
 
 ```bash
-./scripts/verify-pattern1.sh
+./scripts/verify-pattern2.sh
 ```
 
-브라우저에서 `http://localhost:8088`을 열어 로그인한 뒤 보호 API를 호출할 수
-있습니다. SPA는 `http://localhost:8081/api/me`를 직접 호출하며 Spring
-Resource Server가 Bearer JWT를 검증합니다.
+`/token/boundary`는 실제 token 값을 반환하지 않고 서버 저장 여부만 보여줍니다.
+`/token/access`는 access token과 만료 메타데이터만 `no-store`로 전달하며,
+refresh token은 반환하지 않습니다. 브라우저는 이 access token으로
+`http://localhost:8081/api/me`를 직접 호출합니다.
 
-Keycloak의 dedicated audience mapper는 `spa-public` access token에
-`keycloak-pattern-api`를 추가합니다. Spring은 signature, `iss`, `exp`뿐
-아니라 이 `aud`도 검사합니다. `verify-pattern1.sh`는 같은 정상 토큰을
-`deliberately-wrong-audience`를 기대하는 진단 인스턴스에도 제출해 `401`을
-확인합니다.
-
-Keycloak은 `KC_HOSTNAME=http://localhost:8080`을 기준으로 token의 `iss`를
-발급합니다. 정상 Resource Server는 이 외부 issuer 문자열을 검증하되 JWKS는
-Docker 내부의 `http://keycloak:8080`에서 가져옵니다. 진단 인스턴스는 일부러
-`http://wrong-issuer.invalid`를 기대하도록 구성되어, 서명과 audience가
-정상이더라도 issuer mismatch로 `401`을 반환합니다.
-
-token 저장 위치와 XSS 범위는
-[`docs/ap1-token-storage.md`](docs/ap1-token-storage.md)에 정리했습니다.
-E2E는 Web Storage token이 0개임과 동시에 실행 중 fetch hook이 Bearer
-header를 관찰할 수 있음을 재현합니다.
-
-refresh rotation, 소비된 refresh token 재사용, RP-Initiated Logout,
-revocation과 stateless JWT의 차이는
-[`docs/ap1-refresh-logout.md`](docs/ap1-refresh-logout.md)에 정리했으며 같은
-E2E에서 실제 Keycloak 26.7.0 동작을 검증합니다.
+자세한 token 경계와 실험 항목은
+[`docs/ap2-token-boundary.md`](docs/ap2-token-boundary.md)를 참고하세요.

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

@@ -34,10 +34,7 @@ public class SecurityConfig {
     @Bean
     CorsConfigurationSource corsConfigurationSource() {
         CorsConfiguration configuration = new CorsConfiguration();
-        configuration.setAllowedOrigins(List.of(
-            "http://localhost:8088",
-            "http://127.0.0.1:8088"
-        ));
+        configuration.setAllowedOrigins(List.of("http://localhost:8082"));
         configuration.setAllowedMethods(List.of("GET", "OPTIONS"));
         configuration.setAllowedHeaders(List.of("Authorization", "Content-Type"));
 

docker-compose.yml

@@ -86,57 +86,28 @@ services:
       - keycloak-net
     restart: unless-stopped
 
-  app-wrong-audience:
-    profiles:
-      - diagnostics
+  token-mediator:
     build:
-      context: ./backend
+      context: ./token-mediator
     environment:
-      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
-      SECURITY_EXPECTED_AUDIENCE: deliberately-wrong-audience
+      SERVER_PORT: "8082"
+      KEYCLOAK_CLIENT_SECRET: ${TOKEN_MEDIATING_CLIENT_SECRET:?set TOKEN_MEDIATING_CLIENT_SECRET in .env}
     ports:
-      - "127.0.0.1:18081:8081"
+      - "127.0.0.1:8082:8082"
     depends_on:
       keycloak:
         condition: service_healthy
     healthcheck:
       test:
         - CMD-SHELL
-        - wget -q -O - http://127.0.0.1:8081/actuator/health | grep -q '"status":"UP"'
-      interval: 10s
-      timeout: 5s
-      retries: 12
-      start_period: 20s
-    networks:
-      - keycloak-net
-
-  app-wrong-issuer:
-    profiles:
-      - diagnostics
-    build:
-      context: ./backend
-    environment:
-      SERVER_PORT: "8081"
-      SPRING_SECURITY_OAUTH2_RESOURCESERVER_JWT_ISSUER_URI: http://wrong-issuer.invalid/realms/keycloak-patterns
-      SPRING_SECURITY_OAUTH2_RESOURCESERVER_JWT_JWK_SET_URI: http://keycloak:8080/realms/keycloak-patterns/protocol/openid-connect/certs
-      SECURITY_EXPECTED_AUDIENCE: keycloak-pattern-api
-    ports:
-      - "127.0.0.1:18082:8081"
-    depends_on:
-      keycloak:
-        condition: service_healthy
-    healthcheck:
-      test:
-        - CMD-SHELL
-        - wget -q -O - http://127.0.0.1:8081/actuator/health | grep -q '"status":"UP"'
+        - wget -q -O - http://127.0.0.1:8082/actuator/health | grep -q '"status":"UP"'
       interval: 10s
       timeout: 5s
       retries: 12
       start_period: 20s
     networks:
       - keycloak-net
+    restart: unless-stopped
 
   nginx:
     build:

docs/ap1-refresh-logout.md

@@ -1,30 +0,0 @@
-# AP1 refresh rotation and logout
-
-Realm 실행 profile:
-
-- Access Token Lifespan: 300초
-- Revoke Refresh Token: 활성화
-- Refresh Token Max Reuse: 0
-
-`e2e/pattern1.mjs`는 token 원문을 출력하지 않고 다음 순서를 실행한다.
-
-1. browser Authorization Code + PKCE 로그인으로 AT₁/RT₁/ID Token을 받는다.
-2. `signoutRedirect()`가 `id_token_hint`를 포함한 Keycloak logout endpoint를
-   호출하는지 확인한다.
-3. logout 이후 새 authorization 요청에서 로그인 화면이 다시 필요한지
-   확인한다.
-4. 새 RT₁으로 refresh하여 AT₂/RT₂를 받고 RT₂가 RT₁과 다른지 확인한다.
-5. 이미 소비된 RT₁을 재사용해 성공하지 않는지 확인한다.
-6. RT₁ 재사용 뒤 RT₂와 realm session 상태가 어떤 결과를 내는지 status로
-   기록한다. 이 결과를 사전에 family invalidation이라고 단정하지 않는다.
-7. refresh token을 revoke한 뒤 같은 refresh token의 재사용은 실패하지만,
-   이미 발급된 self-contained access JWT는 `exp` 전까지 Resource Server에서
-   계속 `200`인 stateless 함정을 확인한다.
-
-logout은 브라우저 SSO session을 종료하는 흐름이고 token revocation은 특정
-token grant를 폐기하는 흐름이다. 둘은 목적과 endpoint가 다르다.
-
-즉시 access 차단이 필요한 시스템이라면 짧은 access token TTL 외에
-introspection, reference token 또는 별도 deny-list 같은 stateful 검증을
-검토해야 한다. 이 AP1 구현은 JWT의 stateless 검증 특성을 의도적으로
-유지한다.

docs/ap1-token-storage.md

@@ -1,29 +0,0 @@
-# AP1 token storage trade-off
-
-AP1에서는 `access_token`, `refresh_token`, `id_token`을
-`oidc-client-ts`의 명시적인 `InMemoryWebStorage`에만 보관한다.
-`localStorage`와 `sessionStorage`에는 OAuth token을 저장하지 않는다.
-
-full-page authorization redirect를 생존해야 하는 일회성 transaction
-state와 PKCE verifier만 `sessionStorage`를 사용한다. callback 성공 후
-라이브러리가 해당 transaction state를 제거한다.
-
-| 저장 위치 | reload 생존 | JavaScript 접근 | AP1 선택 |
-|---|---:|---:|---:|
-| 메모리 | 아니요 | 실행 중 가능 | 사용 |
-| `sessionStorage` | 같은 탭에서 가능 | 가능 | token 저장 금지 |
-| `localStorage` | 예 | 가능 | token 저장 금지 |
-| HttpOnly cookie | 가능 | raw token 접근 불가 | AP2/AP3의 서버 소유 경계 |
-
-메모리 저장은 XSS를 제거하지 않는다. 악성 스크립트가 실행 중 `fetch`를
-후킹하면 SPA가 붙이는 `Authorization: Bearer ...` 헤더를 관찰할 수 있다.
-다만 persistent storage를 사용하지 않으므로 reload 이후 탈취 가능한 token
-복사본이 남지 않는다.
-
-`e2e/pattern1.mjs`는 다음 두 조건을 동시에 검증한다.
-
-1. access token이 Web Storage 어디에도 존재하지 않는다.
-2. 실행 중 fetch hook은 Bearer token을 관찰할 수 있다.
-
-따라서 결론은 “메모리면 XSS에 안전”이 아니라 “영속 탈취 범위를 줄이지만
-실행 중 XSS에는 여전히 노출”이다.

docs/ap2-token-boundary.md

@@ -0,0 +1,38 @@
+# AP2 · Token-Mediating Backend
+
+## 책임 경계
+
+1. 브라우저는 Spring backend의 `/oauth2/authorization/keycloak`로 로그인을
+   시작합니다.
+2. Keycloak은 authorization code를 Spring callback으로 전달합니다.
+3. confidential client인 Spring backend가 client secret을 사용해 code를
+   교환하고 access/refresh token을 `OAuth2AuthorizedClientService`에
+   보관합니다.
+4. 브라우저가 `/token/access`를 호출하면 backend는 현재 access token,
+   token type, 만료 시각만 `Cache-Control: no-store`로 반환합니다.
+5. 브라우저는 전달받은 access token을 메모리에서만 사용해 Resource
+   Server를 직접 호출합니다.
+
+refresh token은 브라우저 응답, Web Storage, cookie에 전달되지 않습니다.
+access token이 만료되면 `OAuth2AuthorizedClientManager`가 서버에 보관된
+refresh token으로 갱신한 뒤 새 access token만 전달할 수 있습니다.
+
+## 확인할 보안 속성
+
+- Keycloak client는 `client_secret_basic`을 사용하는 confidential client입니다.
+- Resource Server는 서명, issuer, timestamp와 함께
+  `aud=keycloak-pattern-api`를 검증합니다.
+- CORS는 AP2 UI origin인 `http://localhost:8082`의 `GET`만 허용합니다.
+- access-token 응답에는 `refresh_token` 필드가 없고 `no-store`가 적용됩니다.
+- 브라우저 cookie에는 HttpOnly, SameSite=Lax인 `AP2_SESSION` 식별자만
+  저장됩니다. 실제 OAuth token은 session cookie 안에 들어가지 않습니다.
+
+## 실행
+
+```bash
+./scripts/verify-pattern2.sh
+```
+
+검증은 실제 Keycloak 로그인 후 서버 token 보관 여부, access-only 응답의
+필드 집합과 audience, 브라우저의 직접 Resource Server 호출, Web Storage
+비사용을 확인합니다.

e2e/package.json

@@ -4,7 +4,7 @@
   "version": "1.0.0",
   "type": "module",
   "scripts": {
-    "test:pattern1": "node pattern1.mjs"
+    "test:pattern2": "node pattern2.mjs"
   },
   "devDependencies": {
     "playwright-core": "1.62.0"

e2e/pattern1.mjs

@@ -1,210 +0,0 @@
-import assert from "node:assert/strict";
-import { chromium } from "playwright-core";
-
-const username = process.env.E2E_USERNAME ?? "regular-user";
-const password = process.env.E2E_PASSWORD;
-const frontendUrl = "http://localhost:8088/";
-const tokenEndpoint =
-  "http://localhost:8080/realms/keycloak-patterns/protocol/openid-connect/token";
-const revokeEndpoint =
-  "http://localhost:8080/realms/keycloak-patterns/protocol/openid-connect/revoke";
-
-assert.ok(password, "E2E_PASSWORD must be set");
-
-async function login(page) {
-  await page.locator("#login").click();
-  await page.waitForURL(/localhost:8080/u);
-  await page.locator("#username").waitFor();
-
-  const tokenResponsePromise = page.waitForResponse((response) =>
-    response.url() === tokenEndpoint
-    && response.request().postData()?.includes("grant_type=authorization_code"),
-  );
-
-  await page.locator("#username").fill(username);
-  await page.locator("#password").fill(password);
-  await page.locator("#kc-login").click();
-
-  const tokenResponse = await tokenResponsePromise;
-  assert.equal(tokenResponse.status(), 200);
-  const tokenSet = await tokenResponse.json();
-  assert.ok(tokenSet.access_token);
-  assert.ok(tokenSet.refresh_token);
-  assert.ok(tokenSet.id_token);
-
-  await page.waitForURL(frontendUrl);
-  await page.locator('[data-authenticated="true"]').waitFor();
-  return tokenSet;
-}
-
-async function postForm(url, values) {
-  return fetch(url, {
-    method: "POST",
-    headers: { "Content-Type": "application/x-www-form-urlencoded" },
-    body: new URLSearchParams(values),
-  });
-}
-
-async function refresh(refreshToken) {
-  return postForm(tokenEndpoint, {
-    grant_type: "refresh_token",
-    client_id: "spa-public",
-    refresh_token: refreshToken,
-  });
-}
-
-async function callResource(accessToken, url = "http://localhost:8081/api/me") {
-  return fetch(url, {
-    headers: { Authorization: `Bearer ${accessToken}` },
-  });
-}
-
-const browser = await chromium.launch({
-  executablePath: process.env.CHROME_BIN ?? "/usr/bin/google-chrome",
-  headless: true,
-  args: ["--no-sandbox"],
-});
-
-try {
-  const context = await browser.newContext();
-  const page = await context.newPage();
-  let authorizationUrl;
-
-  page.on("request", (request) => {
-    if (request.url().includes("/protocol/openid-connect/auth")) {
-      authorizationUrl = new URL(request.url());
-    }
-  });
-
-  await page.goto(frontendUrl);
-  const firstTokenSet = await login(page);
-
-  assert.equal(authorizationUrl?.searchParams.get("response_type"), "code");
-  assert.equal(authorizationUrl?.searchParams.get("code_challenge_method"), "S256");
-  assert.ok(authorizationUrl?.searchParams.get("code_challenge"));
-
-  await page.evaluate(() => {
-    const originalFetch = window.fetch.bind(window);
-    window.__xssProbe = { authorization: null };
-    window.fetch = (input, init = {}) => {
-      const headers = new Headers(
-        init.headers ?? (input instanceof Request ? input.headers : undefined),
-      );
-      const authorization = headers.get("Authorization");
-      if (authorization) {
-        window.__xssProbe.authorization = authorization;
-      }
-      return originalFetch(input, init);
-    };
-  });
-
-  await page.locator("#call-api").click();
-  await page.waitForFunction(() => {
-    const text = document.querySelector("#result")?.textContent ?? "";
-    return text.includes('"httpStatus": 200');
-  });
-
-  const capturedAuthorization = await page.evaluate(
-    () => window.__xssProbe.authorization,
-  );
-  assert.match(capturedAuthorization, /^Bearer /u);
-  const accessToken = capturedAuthorization.slice("Bearer ".length);
-  assert.equal(accessToken, firstTokenSet.access_token);
-
-  const payload = JSON.parse(
-    Buffer.from(accessToken.split(".")[1], "base64url").toString("utf8"),
-  );
-  const audiences = Array.isArray(payload.aud) ? payload.aud : [payload.aud];
-  assert.ok(audiences.includes("keycloak-pattern-api"));
-
-  const storageSnapshot = await page.evaluate(() => ({
-    localStorage: Object.values(localStorage),
-    sessionStorage: Object.values(sessionStorage),
-  }));
-  assert.equal(JSON.stringify(storageSnapshot).includes(accessToken), false);
-  assert.ok(capturedAuthorization);
-
-  if (process.env.WRONG_AUDIENCE_URL) {
-    assert.equal(
-      (await callResource(accessToken, process.env.WRONG_AUDIENCE_URL)).status,
-      401,
-    );
-  }
-  if (process.env.WRONG_ISSUER_URL) {
-    assert.equal(
-      (await callResource(accessToken, process.env.WRONG_ISSUER_URL)).status,
-      401,
-    );
-  }
-
-  const logoutRequestPromise = page.waitForRequest((request) =>
-    request.url().includes("/protocol/openid-connect/logout"),
-  );
-  await page.locator("#logout").click();
-  const logoutRequest = await logoutRequestPromise;
-  assert.ok(new URL(logoutRequest.url()).searchParams.get("id_token_hint"));
-  await page.waitForURL(frontendUrl);
-  await page.locator('[data-authenticated="false"]').waitFor();
-
-  const secondTokenSet = await login(page);
-  const rotatedResponse = await refresh(secondTokenSet.refresh_token);
-  assert.equal(rotatedResponse.status, 200);
-  const rotated = await rotatedResponse.json();
-  assert.ok(rotated.refresh_token);
-  assert.notEqual(rotated.refresh_token, secondTokenSet.refresh_token);
-
-  const reusedOldResponse = await refresh(secondTokenSet.refresh_token);
-  assert.notEqual(
-    reusedOldResponse.status,
-    200,
-    "a consumed refresh token must not be accepted again",
-  );
-
-  const rotatedAfterReuseResponse = await refresh(rotated.refresh_token);
-  const rotatedAfterReuseStatus = rotatedAfterReuseResponse.status;
-  assert.ok([200, 400, 401].includes(rotatedAfterReuseStatus));
-
-  assert.equal(
-    (await callResource(rotated.access_token)).status,
-    200,
-    "a locally validated access JWT remains usable until exp",
-  );
-
-  await context.clearCookies();
-  await page.reload();
-  await page.locator('[data-authenticated="false"]').waitFor();
-  const thirdTokenSet = await login(page);
-
-  const revokeResponse = await postForm(revokeEndpoint, {
-    token: thirdTokenSet.refresh_token,
-    token_type_hint: "refresh_token",
-    client_id: "spa-public",
-  });
-  assert.equal(revokeResponse.status, 200);
-  assert.notEqual((await refresh(thirdTokenSet.refresh_token)).status, 200);
-  assert.equal(
-    (await callResource(thirdTokenSet.access_token)).status,
-    200,
-    "refresh revoke is not an immediate deny-list for a stateless access JWT",
-  );
-
-  await page.reload();
-  await page.locator('[data-authenticated="false"]').waitFor();
-  assert.equal(
-    await page.evaluate(
-      (token) => JSON.stringify({
-        localStorage: Object.values(localStorage),
-        sessionStorage: Object.values(sessionStorage),
-      }).includes(token),
-      thirdTokenSet.access_token,
-    ),
-    false,
-  );
-
-  console.log(
-    "pattern1 verified: PKCE, aud/iss negatives, memory/XSS boundary, logout, RT rotation/reuse, revoke-vs-stateless JWT"
-      + ` (RT2 after RT1 reuse: ${rotatedAfterReuseStatus})`,
-  );
-} finally {
-  await browser.close();
-}

e2e/pattern2.mjs

@@ -0,0 +1,115 @@
+import assert from "node:assert/strict";
+import { chromium } from "playwright-core";
+
+const password = process.env.E2E_PASSWORD;
+assert.ok(password, "E2E_PASSWORD must be set");
+
+async function completeKeycloakLogin(page) {
+  for (let attempt = 1; attempt <= 2; attempt += 1) {
+    await page.locator("#username").fill(
+      process.env.E2E_USERNAME ?? "regular-user",
+    );
+    await page.locator("#password").fill(password);
+    await page.locator("#kc-login").click();
+    await page.waitForLoadState("domcontentloaded");
+
+    if (page.url() === "http://localhost:8082/") {
+      return;
+    }
+    if (attempt === 1) {
+      await page.goto(
+        "http://localhost:8082/oauth2/authorization/keycloak",
+      );
+      await page.waitForURL(/localhost:8080/u);
+    }
+  }
+  throw new Error(`Keycloak login did not return to AP2: ${page.url()}`);
+}
+
+const browser = await chromium.launch({
+  executablePath: process.env.CHROME_BIN ?? "/usr/bin/google-chrome",
+  headless: true,
+  args: ["--no-sandbox"],
+});
+
+try {
+  const context = await browser.newContext();
+  const page = await context.newPage();
+
+  await page.goto("http://localhost:8082");
+  await page.locator("#login").click();
+  await page.waitForURL(/localhost:8080/u);
+  await completeKeycloakLogin(page);
+
+  const boundaryResponsePromise = page.waitForResponse((response) =>
+    response.url().endsWith("/token/boundary"),
+  );
+  await page.locator("#inspect").click();
+  const boundaryResponse = await boundaryResponsePromise;
+  assert.equal(boundaryResponse.status(), 200);
+  const boundary = await boundaryResponse.json();
+
+  assert.equal(boundary.accessTokenStored, true);
+  assert.equal(boundary.refreshTokenStored, true);
+  assert.equal(boundary.browserReceivesRefreshToken, false);
+  assert.equal(JSON.stringify(boundary).includes("refresh_token"), false);
+
+  const accessResponsePromise = page.waitForResponse((response) =>
+    response.url().endsWith("/token/access"),
+  );
+  const resourceResponsePromise = page.waitForResponse(
+    (response) =>
+      response.url() === "http://localhost:8081/api/me" &&
+      response.request().method() === "GET",
+  );
+  await page.locator("#call-api").click();
+
+  const accessResponse = await accessResponsePromise;
+  assert.equal(accessResponse.status(), 200);
+  assert.match(accessResponse.headers()["cache-control"], /no-store/u);
+  const accessHandoff = await accessResponse.json();
+  assert.deepEqual(
+    Object.keys(accessHandoff).sort(),
+    ["access_token", "expires_at", "token_type"],
+  );
+  assert.equal(accessHandoff.token_type, "Bearer");
+  assert.equal(typeof accessHandoff.access_token, "string");
+  assert.ok(accessHandoff.access_token.length > 100);
+  assert.equal(JSON.stringify(accessHandoff).includes("refresh_token"), false);
+
+  const [, payload] = accessHandoff.access_token.split(".");
+  const claims = JSON.parse(
+    Buffer.from(payload, "base64url").toString("utf8"),
+  );
+  const audience = Array.isArray(claims.aud) ? claims.aud : [claims.aud];
+  assert.ok(audience.includes("keycloak-pattern-api"));
+
+  const resourceResponse = await resourceResponsePromise;
+  assert.equal(resourceResponse.status(), 200);
+  const resource = await resourceResponse.json();
+  assert.equal(resource.username, "regular-user");
+  assert.ok(resource.audience.includes("keycloak-pattern-api"));
+  await page.locator("#result").getByText('"resourceApiStatus": 200').waitFor();
+
+  const cookies = await context.cookies("http://localhost:8082/");
+  const sessionCookie = cookies.find((cookie) => cookie.name === "AP2_SESSION");
+  assert.ok(sessionCookie);
+  assert.equal(sessionCookie.httpOnly, true);
+  assert.equal(sessionCookie.sameSite, "Lax");
+
+  const storage = await page.evaluate(() => ({
+    localStorage: Object.values(localStorage),
+    sessionStorage: Object.values(sessionStorage),
+  }));
+  assert.equal(JSON.stringify(storage).includes("refresh_token"), false);
+  assert.equal(
+    JSON.stringify(storage).includes(accessHandoff.access_token),
+    false,
+  );
+
+  console.log(
+    "pattern2 verified: server refresh custody, access-only handoff, direct browser resource call",
+  );
+} finally {
+  await browser.close();
+}

frontend/Dockerfile

@@ -1,16 +1,4 @@
-FROM node:24-alpine AS build
-
-WORKDIR /workspace
-
-COPY package.json package-lock.json ./
-RUN npm ci
-
-COPY src ./src
-COPY test ./test
-RUN npm test && npm run build
-
 FROM nginx:1.29-alpine
 
 COPY nginx.conf /etc/nginx/conf.d/default.conf
 COPY index.html /usr/share/nginx/html/index.html
-COPY --from=build /workspace/dist/app.js /usr/share/nginx/html/app.js

frontend/index.html

@@ -3,66 +3,31 @@
 <head>
   <meta charset="utf-8">
   <meta name="viewport" content="width=device-width, initial-scale=1">
-  <meta name="referrer" content="no-referrer">
-  <title>AP1 · SPA Direct + Resource Server</title>
+  <title>Keycloak Authentication Patterns</title>
   <style>
     :root {
       color-scheme: light dark;
       font-family: system-ui, sans-serif;
     }
     body {
-      max-width: 56rem;
-      margin: 6vh auto;
+      max-width: 48rem;
+      margin: 8vh auto;
       padding: 0 1.5rem;
-      line-height: 1.55;
-    }
-    button {
-      margin: 0 0.5rem 0.5rem 0;
-      padding: 0.6rem 0.9rem;
-      cursor: pointer;
-    }
-    code, pre {
-      border-radius: 0.35rem;
-      background: color-mix(in srgb, CanvasText 9%, Canvas);
+      line-height: 1.6;
     }
     code {
-      padding: 0.1rem 0.3rem;
-    }
-    pre {
-      min-height: 8rem;
-      padding: 1rem;
-      overflow: auto;
-      white-space: pre-wrap;
-    }
-    .notice {
-      border-left: 0.3rem solid #e09f3e;
-      padding-left: 1rem;
+      padding: 0.15rem 0.35rem;
+      border-radius: 0.25rem;
+      background: color-mix(in srgb, CanvasText 10%, Canvas);
     }
   </style>
 </head>
 <body>
-  <main>
-    <h1>AP1 · SPA Direct + Resource Server</h1>
-    <p>
-      바닐라 JavaScript SPA가 <code>spa-public</code> client로 Authorization
-      Code + PKCE를 수행하고, access token을 직접 Spring Resource Server에
-      전달합니다.
-    </p>
-    <p class="notice">
-      access/refresh token은 메모리에만 존재합니다. 새로고침하면 사라지는 것이
-      이 패턴의 의도된 보안 경계입니다.
-    </p>
-
-    <section>
-      <button id="login" type="button">Keycloak 로그인</button>
-      <button id="call-api" type="button" disabled>보호 API 호출</button>
-      <button id="pkce-demo" type="button">수동 PKCE 생성</button>
-      <button id="logout" type="button" disabled>로그아웃</button>
-    </section>
-
-    <p id="session-state" data-authenticated="false">세션 확인 중…</p>
-    <pre id="result" aria-live="polite"></pre>
-  </main>
-  <script type="module" src="/app.js"></script>
+  <h1>Keycloak Authentication Patterns</h1>
+  <p>공통 Docker Compose baseline이 실행 중입니다.</p>
+  <p>
+    공개 API는 <code>/api/public</code>, 보호 API는
+    <code>/api/me</code>에서 확인할 수 있습니다.
+  </p>
 </body>
 </html>

frontend/nginx.conf

@@ -21,7 +21,6 @@ server {
     }
 
     location / {
-        add_header Cache-Control "no-store";
         try_files $uri $uri/ /index.html;
     }
 }

frontend/package-lock.json

@@ -1,523 +0,0 @@
-{
-  "name": "keycloak-pattern1-spa",
-  "version": "1.0.0",
-  "lockfileVersion": 3,
-  "requires": true,
-  "packages": {
-    "": {
-      "name": "keycloak-pattern1-spa",
-      "version": "1.0.0",
-      "dependencies": {
-        "oidc-client-ts": "3.5.0"
-      },
-      "devDependencies": {
-        "esbuild": "0.28.1"
-      }
-    },
-    "node_modules/@esbuild/aix-ppc64": {
-      "version": "0.28.1",
-      "resolved": "https://registry.npmjs.org/@esbuild/aix-ppc64/-/aix-ppc64-0.28.1.tgz",
-      "integrity": "sha512-Svl7tq8k/08+p6CXPpRjQ1fKX+1odH/BQbb48fV6fj3CWHhsoIOoY87w1oHXm0qEpkIK3ZfVgp0hed3XBXzXMQ==",
-      "cpu": [
-        "ppc64"
-      ],
-      "dev": true,
-      "license": "MIT",
-      "optional": true,
-      "os": [
-        "aix"
-      ],
-      "engines": {
-        "node": ">=18"
-      }
-    },
-    "node_modules/@esbuild/android-arm": {
-      "version": "0.28.1",
-      "resolved": "https://registry.npmjs.org/@esbuild/android-arm/-/android-arm-0.28.1.tgz",
-      "integrity": "sha512-0k2F129Xdio1TdJfzJ8sy1Q47vUD2NnwdhiAf7drUN1EBTfPf4hsFCtmMgu/6m8JSzsBrlmVjudMBQqOfG8usQ==",
-      "cpu": [
-        "arm"
-      ],
-      "dev": true,
-      "license": "MIT",
-      "optional": true,
-      "os": [
-        "android"
-      ],
-      "engines": {
-        "node": ">=18"
-      }
-    },
-    "node_modules/@esbuild/android-arm64": {
-      "version": "0.28.1",
-      "resolved": "https://registry.npmjs.org/@esbuild/android-arm64/-/android-arm64-0.28.1.tgz",
-      "integrity": "sha512-34EGEbCIAgosYz6goLcopX6Mo7NyGv9tfwEM2/7Ce2VcVRk568iSvniGWcUXIy7wEDR1wzolcxcriFVrWYcwBg==",
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-        "@esbuild/win32-ia32": "0.28.1",
-        "@esbuild/win32-x64": "0.28.1"
-      }
-    },
-    "node_modules/jwt-decode": {
-      "version": "4.0.0",
-      "resolved": "https://registry.npmjs.org/jwt-decode/-/jwt-decode-4.0.0.tgz",
-      "integrity": "sha512-+KJGIyHgkGuIq3IEBNftfhW/LfWhXUIY6OmyVWjliu5KH1y0fw7VQ8YndE2O4qZdMSd9SqbnC8GOcZEy0Om7sA==",
-      "license": "MIT",
-      "engines": {
-        "node": ">=18"
-      }
-    },
-    "node_modules/oidc-client-ts": {
-      "version": "3.5.0",
-      "resolved": "https://registry.npmjs.org/oidc-client-ts/-/oidc-client-ts-3.5.0.tgz",
-      "integrity": "sha512-l2q8l9CTCTOlbX+AnK4p3M+4CEpKpyQhle6blQkdFhm0IsBqsxm15bYaSa11G7pWdsYr6epdsRZxJpCyCRbT8A==",
-      "license": "Apache-2.0",
-      "dependencies": {
-        "jwt-decode": "^4.0.0"
-      },
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-  }
-}

frontend/package.json

@@ -1,16 +0,0 @@
-{
-  "name": "keycloak-pattern1-spa",
-  "private": true,
-  "version": "1.0.0",
-  "type": "module",
-  "scripts": {
-    "build": "esbuild src/app.js --bundle --format=esm --outfile=dist/app.js --minify --sourcemap",
-    "test": "node --test test/*.test.mjs"
-  },
-  "dependencies": {
-    "oidc-client-ts": "3.5.0"
-  },
-  "devDependencies": {
-    "esbuild": "0.28.1"
-  }
-}

frontend/src/app.js

@@ -1,131 +0,0 @@
-import {
-  InMemoryWebStorage,
-  UserManager,
-  WebStorageStateStore,
-} from "oidc-client-ts";
-
-import { createPkcePair } from "./pkce.js";
-
-const authority = "http://localhost:8080/realms/keycloak-patterns";
-const backendBaseUrl = "http://localhost:8081";
-
-const userManager = new UserManager({
-  authority,
-  client_id: "spa-public",
-  redirect_uri: "http://localhost:8088/callback.html",
-  post_logout_redirect_uri: "http://localhost:8088/",
-  response_type: "code",
-  scope: "openid profile email",
-  automaticSilentRenew: true,
-  monitorSession: false,
-  loadUserInfo: false,
-  userStore: new WebStorageStateStore({
-    store: new InMemoryWebStorage(),
-  }),
-  stateStore: new WebStorageStateStore({
-    store: window.sessionStorage,
-  }),
-});
-
-const loginButton = document.querySelector("#login");
-const logoutButton = document.querySelector("#logout");
-const apiButton = document.querySelector("#call-api");
-const pkceButton = document.querySelector("#pkce-demo");
-const sessionState = document.querySelector("#session-state");
-const result = document.querySelector("#result");
-
-let currentUser = null;
-
-function renderJson(value) {
-  result.textContent = JSON.stringify(value, null, 2);
-}
-
-function tokenMetadata(user) {
-  return {
-    subject: user.profile.sub,
-    username: user.profile.preferred_username,
-    expiresAt: new Date(user.expires_at * 1000).toISOString(),
-    accessTokenHeldBy: "browser memory",
-    refreshTokenHeldBy: user.refresh_token ? "browser memory" : "not issued",
-  };
-}
-
-function renderSession(user) {
-  currentUser = user;
-  const authenticated = Boolean(user && !user.expired);
-  sessionState.dataset.authenticated = String(authenticated);
-  sessionState.textContent = authenticated
-    ? `${user.profile.preferred_username} 로그인됨 · token은 메모리에만 보관`
-    : "로그인되지 않음 · 브라우저 저장소에 token 없음";
-  loginButton.disabled = authenticated;
-  logoutButton.disabled = !authenticated;
-  apiButton.disabled = !authenticated;
-
-  if (authenticated) {
-    renderJson(tokenMetadata(user));
-  }
-}
-
-async function finishSigninCallback() {
-  const params = new URLSearchParams(window.location.search);
-  const isCallback = window.location.pathname === "/callback.html"
-    && (params.has("code") || params.has("error"));
-
-  if (!isCallback) {
-    return null;
-  }
-
-  const user = await userManager.signinRedirectCallback();
-  window.history.replaceState({}, document.title, "/");
-  return user;
-}
-
-async function callProtectedApi() {
-  if (!currentUser || currentUser.expired) {
-    throw new Error("로그인이 필요합니다.");
-  }
-
-  const response = await fetch(`${backendBaseUrl}/api/me`, {
-    headers: {
-      Authorization: `Bearer ${currentUser.access_token}`,
-    },
-  });
-  const body = await response.json();
-  renderJson({
-    httpStatus: response.status,
-    resourceServerResponse: body,
-    tokenBoundary: tokenMetadata(currentUser),
-  });
-
-  if (!response.ok) {
-    throw new Error(`보호 API가 ${response.status}를 반환했습니다.`);
-  }
-}
-
-loginButton.addEventListener("click", () => userManager.signinRedirect());
-logoutButton.addEventListener("click", () => userManager.signoutRedirect());
-apiButton.addEventListener("click", () => {
-  callProtectedApi().catch((error) => renderJson({ error: error.message }));
-});
-pkceButton.addEventListener("click", () => {
-  createPkcePair()
-    .then(({ verifier, challenge, method }) => renderJson({
-      method,
-      verifierLength: verifier.length,
-      challengeLength: challenge.length,
-      note: "실제 로그인에서는 oidc-client-ts가 같은 S256 단계를 수행합니다.",
-    }))
-    .catch((error) => renderJson({ error: error.message }));
-});
-
-userManager.events.addUserLoaded(renderSession);
-userManager.events.addUserUnloaded(() => renderSession(null));
-userManager.events.addAccessTokenExpired(() => renderSession(null));
-
-try {
-  const callbackUser = await finishSigninCallback();
-  renderSession(callbackUser ?? await userManager.getUser());
-} catch (error) {
-  renderSession(null);
-  renderJson({ error: error.message });
-}

frontend/src/pkce.js

@@ -1,26 +0,0 @@
-function base64Url(bytes) {
-  let binary = "";
-  for (const byte of bytes) {
-    binary += String.fromCharCode(byte);
-  }
-  return btoa(binary)
-    .replaceAll("+", "-")
-    .replaceAll("/", "_")
-    .replace(/=+$/u, "");
-}
-
-export async function createPkcePair(cryptoApi = globalThis.crypto) {
-  const verifierBytes = new Uint8Array(32);
-  cryptoApi.getRandomValues(verifierBytes);
-  const verifier = base64Url(verifierBytes);
-  const digest = await cryptoApi.subtle.digest(
-    "SHA-256",
-    new TextEncoder().encode(verifier),
-  );
-
-  return {
-    verifier,
-    challenge: base64Url(new Uint8Array(digest)),
-    method: "S256",
-  };
-}

frontend/test/pkce.test.mjs

@@ -1,18 +0,0 @@
-import assert from "node:assert/strict";
-import { webcrypto } from "node:crypto";
-import test from "node:test";
-
-globalThis.btoa = (value) => Buffer.from(value, "binary").toString("base64");
-
-const { createPkcePair } = await import("../src/pkce.js");
-
-test("manual PKCE helper creates an RFC 7636 S256 pair", async () => {
-  const pair = await createPkcePair(webcrypto);
-
-  assert.equal(pair.method, "S256");
-  assert.equal(pair.verifier.length, 43);
-  assert.equal(pair.challenge.length, 43);
-  assert.match(pair.verifier, /^[A-Za-z0-9_-]+$/u);
-  assert.match(pair.challenge, /^[A-Za-z0-9_-]+$/u);
-  assert.notEqual(pair.verifier, pair.challenge);
-});

keycloak/import/keycloak-patterns-realm.json

@@ -51,22 +51,7 @@
       "attributes": {
         "pkce.code.challenge.method": "S256",
         "post.logout.redirect.uris": "http://localhost:8088/*##http://127.0.0.1:8088/*"
-      },
-      "protocolMappers": [
-        {
-          "name": "keycloak-pattern-api-audience",
-          "protocol": "openid-connect",
-          "protocolMapper": "oidc-audience-mapper",
-          "consentRequired": false,
-          "config": {
-            "included.custom.audience": "keycloak-pattern-api",
-            "id.token.claim": "false",
-            "access.token.claim": "true",
-            "userinfo.token.claim": "false",
-            "introspection.token.claim": "true"
-          }
-        }
-      ]
+      }
     },
     {
       "clientId": "token-mediating-confidential",
@@ -90,7 +75,22 @@
       ],
       "attributes": {
         "post.logout.redirect.uris": "http://localhost:8082/*"
-      }
+      },
+      "protocolMappers": [
+        {
+          "name": "keycloak-pattern-api-audience",
+          "protocol": "openid-connect",
+          "protocolMapper": "oidc-audience-mapper",
+          "consentRequired": false,
+          "config": {
+            "included.custom.audience": "keycloak-pattern-api",
+            "id.token.claim": "false",
+            "access.token.claim": "true",
+            "userinfo.token.claim": "false",
+            "introspection.token.claim": "true"
+          }
+        }
+      ]
     },
     {
       "clientId": "bff-confidential",

scripts/validate-realm.py

@@ -70,18 +70,6 @@ def validate(path: Path, runtime: bool) -> None:
         spa.get("attributes", {}).get("pkce.code.challenge.method") == "S256",
         "spa-public must enforce PKCE S256",
     )
-    audience_mappers = [
-        mapper
-        for mapper in spa.get("protocolMappers", [])
-        if mapper.get("protocolMapper") == "oidc-audience-mapper"
-    ]
-    if not runtime:
-        require(len(audience_mappers) == 1, "spa-public must declare one audience mapper")
-        require(
-            audience_mappers[0].get("config", {}).get("included.custom.audience")
-            == "keycloak-pattern-api",
-            "spa-public access token must target keycloak-pattern-api",
-        )
 
     for client_id, placeholder in CONFIDENTIAL_CLIENTS.items():
         client = clients[client_id]

scripts/verify-pattern1.sh

@@ -1,26 +0,0 @@
-#!/usr/bin/env sh
-set -eu
-
-if [ ! -f .env ]; then
-  echo "missing .env; copy .env.example and set local-only values" >&2
-  exit 1
-fi
-
-set -a
-. ./.env
-set +a
-
-docker compose down --volumes --remove-orphans
-docker compose up --build -d --wait
-docker compose --profile diagnostics up -d --wait \
-  app-wrong-audience \
-  app-wrong-issuer
-
-npm --prefix e2e ci
-E2E_USERNAME=regular-user \
-E2E_PASSWORD="$REGULAR_USER_PASSWORD" \
-WRONG_AUDIENCE_URL=http://localhost:18081/api/me \
-WRONG_ISSUER_URL=http://localhost:18082/api/me \
-  npm --prefix e2e run test:pattern1
-
-echo "AP1 verified end to end"

scripts/verify-pattern2.sh

@@ -0,0 +1,21 @@
+#!/usr/bin/env sh
+set -eu
+
+if [ ! -f .env ]; then
+  echo "missing .env; copy .env.example and set development values" >&2
+  exit 1
+fi
+
+set -a
+. ./.env
+set +a
+
+docker compose down --volumes --remove-orphans
+docker compose up --build -d --wait
+
+npm --prefix e2e ci
+E2E_USERNAME=regular-user \
+E2E_PASSWORD="$REGULAR_USER_PASSWORD" \
+  npm --prefix e2e run test:pattern2
+
+echo "AP2 confidential client boundary verified"

token-mediator/.dockerignore

@@ -0,0 +1 @@
+target/

token-mediator/Dockerfile

@@ -0,0 +1,17 @@
+FROM maven:3.9.11-eclipse-temurin-21-alpine AS build
+
+WORKDIR /workspace
+COPY pom.xml .
+RUN mvn --batch-mode dependency:go-offline
+COPY src src
+RUN mvn --batch-mode verify
+
+FROM eclipse-temurin:21-jre-alpine
+
+RUN addgroup -S spring && adduser -S spring -G spring
+WORKDIR /app
+COPY --from=build /workspace/target/keycloak-token-mediator.jar app.jar
+USER spring:spring
+
+EXPOSE 8082
+ENTRYPOINT ["java", "-jar", "/app/app.jar"]

token-mediator/pom.xml

@@ -0,0 +1,58 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+
+    <parent>
+        <groupId>org.springframework.boot</groupId>
+        <artifactId>spring-boot-starter-parent</artifactId>
+        <version>3.5.16</version>
+        <relativePath/>
+    </parent>
+
+    <groupId>com.example</groupId>
+    <artifactId>keycloak-token-mediator</artifactId>
+    <version>0.0.1-SNAPSHOT</version>
+    <name>keycloak-token-mediator</name>
+
+    <properties>
+        <java.version>21</java.version>
+    </properties>
+
+    <dependencies>
+        <dependency>
+            <groupId>org.springframework.boot</groupId>
+            <artifactId>spring-boot-starter-actuator</artifactId>
+        </dependency>
+        <dependency>
+            <groupId>org.springframework.boot</groupId>
+            <artifactId>spring-boot-starter-oauth2-client</artifactId>
+        </dependency>
+        <dependency>
+            <groupId>org.springframework.boot</groupId>
+            <artifactId>spring-boot-starter-web</artifactId>
+        </dependency>
+
+        <dependency>
+            <groupId>org.springframework.boot</groupId>
+            <artifactId>spring-boot-starter-test</artifactId>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.springframework.security</groupId>
+            <artifactId>spring-security-test</artifactId>
+            <scope>test</scope>
+        </dependency>
+    </dependencies>
+
+    <build>
+        <finalName>keycloak-token-mediator</finalName>
+        <plugins>
+            <plugin>
+                <groupId>org.springframework.boot</groupId>
+                <artifactId>spring-boot-maven-plugin</artifactId>
+            </plugin>
+        </plugins>
+    </build>
+</project>

token-mediator/src/main/java/com/example/keycloakpattern/mediator/AccessTokenController.java

@@ -0,0 +1,56 @@
+package com.example.keycloakpattern.mediator;
+
+import java.util.LinkedHashMap;
+import java.util.Map;
+
+import org.springframework.http.CacheControl;
+import org.springframework.http.ResponseEntity;
+import org.springframework.security.core.Authentication;
+import org.springframework.security.oauth2.client.OAuth2AuthorizeRequest;
+import org.springframework.security.oauth2.client.OAuth2AuthorizedClient;
+import org.springframework.security.oauth2.client.OAuth2AuthorizedClientManager;
+import org.springframework.security.oauth2.core.OAuth2AccessToken;
+import org.springframework.web.bind.annotation.GetMapping;
+import org.springframework.web.bind.annotation.RestController;
+import org.springframework.web.server.ResponseStatusException;
+
+import static org.springframework.http.HttpStatus.UNAUTHORIZED;
+
+@RestController
+public class AccessTokenController {
+
+    private final OAuth2AuthorizedClientManager authorizedClientManager;
+
+    public AccessTokenController(OAuth2AuthorizedClientManager authorizedClientManager) {
+        this.authorizedClientManager = authorizedClientManager;
+    }
+
+    @GetMapping("/token/access")
+    ResponseEntity<Map<String, Object>> accessToken(Authentication authentication) {
+        OAuth2AuthorizeRequest request = OAuth2AuthorizeRequest
+            .withClientRegistrationId("keycloak")
+            .principal(authentication)
+            .build();
+        OAuth2AuthorizedClient client = authorizedClientManager.authorize(request);
+        if (client == null || client.getAccessToken() == null) {
+            throw new ResponseStatusException(
+                UNAUTHORIZED,
+                "No authorized Keycloak client is available"
+            );
+        }
+
+        OAuth2AccessToken token = client.getAccessToken();
+        Map<String, Object> response = new LinkedHashMap<>();
+        response.put("access_token", token.getTokenValue());
+        response.put("token_type", token.getTokenType().getValue());
+        response.put(
+            "expires_at",
+            token.getExpiresAt() == null ? null : token.getExpiresAt().toString()
+        );
+
+        return ResponseEntity.ok()
+            .cacheControl(CacheControl.noStore())
+            .header("Pragma", "no-cache")
+            .body(response);
+    }
+}

token-mediator/src/main/java/com/example/keycloakpattern/mediator/SecurityConfig.java

@@ -0,0 +1,55 @@
+package com.example.keycloakpattern.mediator;
+
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.security.config.annotation.web.builders.HttpSecurity;
+import org.springframework.security.oauth2.client.AuthorizedClientServiceOAuth2AuthorizedClientManager;
+import org.springframework.security.oauth2.client.OAuth2AuthorizedClientManager;
+import org.springframework.security.oauth2.client.OAuth2AuthorizedClientProvider;
+import org.springframework.security.oauth2.client.OAuth2AuthorizedClientProviderBuilder;
+import org.springframework.security.oauth2.client.OAuth2AuthorizedClientService;
+import org.springframework.security.oauth2.client.registration.ClientRegistrationRepository;
+import org.springframework.security.web.SecurityFilterChain;
+
+@Configuration
+public class SecurityConfig {
+
+    @Bean
+    SecurityFilterChain mediatorSecurity(HttpSecurity http) throws Exception {
+        return http
+            .authorizeHttpRequests(authorize -> authorize
+                .requestMatchers(
+                    "/",
+                    "/index.html",
+                    "/app.js",
+                    "/favicon.ico",
+                    "/actuator/health",
+                    "/actuator/health/**"
+                )
+                .permitAll()
+                .anyRequest()
+                .authenticated())
+            .oauth2Login(oauth2 -> oauth2.defaultSuccessUrl("/", true))
+            .build();
+    }
+
+    @Bean
+    OAuth2AuthorizedClientManager authorizedClientManager(
+        ClientRegistrationRepository clientRegistrationRepository,
+        OAuth2AuthorizedClientService authorizedClientService
+    ) {
+        OAuth2AuthorizedClientProvider authorizedClientProvider =
+            OAuth2AuthorizedClientProviderBuilder.builder()
+                .authorizationCode()
+                .refreshToken()
+                .build();
+
+        AuthorizedClientServiceOAuth2AuthorizedClientManager manager =
+            new AuthorizedClientServiceOAuth2AuthorizedClientManager(
+                clientRegistrationRepository,
+                authorizedClientService
+            );
+        manager.setAuthorizedClientProvider(authorizedClientProvider);
+        return manager;
+    }
+}

token-mediator/src/main/java/com/example/keycloakpattern/mediator/TokenBoundaryController.java

@@ -0,0 +1,44 @@
+package com.example.keycloakpattern.mediator;
+
+import java.util.LinkedHashMap;
+import java.util.Map;
+
+import org.springframework.http.CacheControl;
+import org.springframework.http.ResponseEntity;
+import org.springframework.security.core.Authentication;
+import org.springframework.security.oauth2.client.OAuth2AuthorizedClient;
+import org.springframework.security.oauth2.client.OAuth2AuthorizedClientService;
+import org.springframework.web.bind.annotation.GetMapping;
+import org.springframework.web.bind.annotation.RestController;
+
+@RestController
+public class TokenBoundaryController {
+
+    private final OAuth2AuthorizedClientService authorizedClientService;
+
+    public TokenBoundaryController(
+        OAuth2AuthorizedClientService authorizedClientService
+    ) {
+        this.authorizedClientService = authorizedClientService;
+    }
+
+    @GetMapping("/token/boundary")
+    ResponseEntity<Map<String, Object>> tokenBoundary(Authentication authentication) {
+        OAuth2AuthorizedClient client = authorizedClientService.loadAuthorizedClient(
+            "keycloak",
+            authentication.getName()
+        );
+
+        Map<String, Object> response = new LinkedHashMap<>();
+        response.put("pattern", "AP2-token-mediating-backend");
+        response.put("principal", authentication.getName());
+        response.put("accessTokenStored", client != null && client.getAccessToken() != null);
+        response.put("refreshTokenStored", client != null && client.getRefreshToken() != null);
+        response.put("browserReceivesRefreshToken", false);
+
+        return ResponseEntity.ok()
+            .cacheControl(CacheControl.noStore())
+            .header("Pragma", "no-cache")
+            .body(response);
+    }
+}

token-mediator/src/main/java/com/example/keycloakpattern/mediator/TokenMediatorApplication.java

@@ -0,0 +1,12 @@
+package com.example.keycloakpattern.mediator;
+
+import org.springframework.boot.SpringApplication;
+import org.springframework.boot.autoconfigure.SpringBootApplication;
+
+@SpringBootApplication
+public class TokenMediatorApplication {
+
+    public static void main(String[] args) {
+        SpringApplication.run(TokenMediatorApplication.class, args);
+    }
+}

token-mediator/src/main/resources/application.yml

@@ -0,0 +1,44 @@
+server:
+  port: ${SERVER_PORT:8082}
+  servlet:
+    session:
+      cookie:
+        name: AP2_SESSION
+        http-only: true
+        same-site: lax
+
+spring:
+  application:
+    name: keycloak-token-mediator
+  security:
+    oauth2:
+      client:
+        registration:
+          keycloak:
+            provider: keycloak
+            client-id: token-mediating-confidential
+            client-secret: ${KEYCLOAK_CLIENT_SECRET}
+            client-authentication-method: client_secret_basic
+            authorization-grant-type: authorization_code
+            redirect-uri: "{baseUrl}/login/oauth2/code/{registrationId}"
+            scope:
+              - openid
+              - profile
+              - email
+        provider:
+          keycloak:
+            authorization-uri: http://localhost:8080/realms/keycloak-patterns/protocol/openid-connect/auth
+            token-uri: http://keycloak:8080/realms/keycloak-patterns/protocol/openid-connect/token
+            jwk-set-uri: http://keycloak:8080/realms/keycloak-patterns/protocol/openid-connect/certs
+            user-info-uri: http://keycloak:8080/realms/keycloak-patterns/protocol/openid-connect/userinfo
+            user-name-attribute: preferred_username
+
+management:
+  endpoint:
+    health:
+      probes:
+        enabled: true
+  endpoints:
+    web:
+      exposure:
+        include: health,info

token-mediator/src/main/resources/static/app.js

@@ -0,0 +1,50 @@
+const result = document.querySelector("#result");
+
+function render(value) {
+  result.textContent = JSON.stringify(value, null, 2);
+}
+
+document.querySelector("#login").addEventListener("click", () => {
+  window.location.assign("/oauth2/authorization/keycloak");
+});
+
+document.querySelector("#inspect").addEventListener("click", async () => {
+  const response = await fetch("/token/boundary", {
+    headers: { Accept: "application/json" },
+  });
+  if (response.redirected || response.status === 401) {
+    window.location.assign("/oauth2/authorization/keycloak");
+    return;
+  }
+  render(await response.json());
+});
+
+document.querySelector("#call-api").addEventListener("click", async () => {
+  const tokenResponse = await fetch("/token/access", {
+    headers: { Accept: "application/json" },
+  });
+  if (tokenResponse.redirected || tokenResponse.status === 401) {
+    window.location.assign("/oauth2/authorization/keycloak");
+    return;
+  }
+  if (!tokenResponse.ok) {
+    render({ tokenEndpointStatus: tokenResponse.status });
+    return;
+  }
+
+  const { access_token: accessToken, expires_at: expiresAt } =
+    await tokenResponse.json();
+  const apiResponse = await fetch("http://localhost:8081/api/me", {
+    headers: {
+      Accept: "application/json",
+      Authorization: `Bearer ${accessToken}`,
+    },
+  });
+  render({
+    accessTokenHeldInMemoryOnly: true,
+    refreshTokenReceived: false,
+    accessTokenExpiresAt: expiresAt,
+    resourceApiStatus: apiResponse.status,
+    resource: await apiResponse.json(),
+  });
+});

token-mediator/src/main/resources/static/index.html

@@ -0,0 +1,30 @@
+<!doctype html>
+<html lang="ko">
+<head>
+  <meta charset="utf-8">
+  <meta name="viewport" content="width=device-width, initial-scale=1">
+  <title>AP2 · Token-Mediating Backend</title>
+  <style>
+    :root { color-scheme: light dark; font-family: system-ui, sans-serif; }
+    body { max-width: 52rem; margin: 6vh auto; padding: 0 1.5rem; line-height: 1.6; }
+    button { margin-right: 0.5rem; padding: 0.6rem 0.9rem; cursor: pointer; }
+    pre { min-height: 8rem; padding: 1rem; border-radius: 0.4rem;
+      background: color-mix(in srgb, CanvasText 9%, Canvas); white-space: pre-wrap; }
+  </style>
+</head>
+<body>
+  <main>
+    <h1>AP2 · Token-Mediating Backend</h1>
+    <p>
+      confidential backend가 authorization code를 token으로 교환합니다.
+      refresh token은 서버의 <code>OAuth2AuthorizedClientService</code>에만
+      보관됩니다.
+    </p>
+    <button id="login" type="button">Keycloak 로그인</button>
+    <button id="inspect" type="button">서버 token 경계 확인</button>
+    <button id="call-api" type="button">access token으로 API 직접 호출</button>
+    <pre id="result" aria-live="polite"></pre>
+  </main>
+  <script type="module" src="/app.js"></script>
+</body>
+</html>

token-mediator/src/test/java/com/example/keycloakpattern/mediator/TokenBoundaryControllerTest.java

@@ -0,0 +1,84 @@
+package com.example.keycloakpattern.mediator;
+
+import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.when;
+import static org.springframework.security.test.web.servlet.request.SecurityMockMvcRequestPostProcessors.oidcLogin;
+import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.get;
+import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.header;
+import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.jsonPath;
+import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.status;
+
+import java.time.Instant;
+
+import org.junit.jupiter.api.Test;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.test.autoconfigure.web.servlet.AutoConfigureMockMvc;
+import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.security.oauth2.client.OAuth2AuthorizeRequest;
+import org.springframework.security.oauth2.client.OAuth2AuthorizedClient;
+import org.springframework.security.oauth2.client.OAuth2AuthorizedClientManager;
+import org.springframework.security.oauth2.client.OAuth2AuthorizedClientService;
+import org.springframework.security.oauth2.core.OAuth2AccessToken;
+import org.springframework.security.oauth2.core.OAuth2RefreshToken;
+import org.springframework.test.context.bean.override.mockito.MockitoBean;
+import org.springframework.test.web.servlet.MockMvc;
+
+@SpringBootTest(properties = "KEYCLOAK_CLIENT_SECRET=test-only-secret")
+@AutoConfigureMockMvc
+class TokenBoundaryControllerTest {
+
+    @Autowired
+    private MockMvc mockMvc;
+
+    @MockitoBean
+    private OAuth2AuthorizedClientService authorizedClientService;
+
+    @MockitoBean
+    private OAuth2AuthorizedClientManager authorizedClientManager;
+
+    @Test
+    void reportsServerSideTokensWithoutReturningTheirValues() throws Exception {
+        OAuth2AuthorizedClient client = mock(OAuth2AuthorizedClient.class);
+        when(client.getAccessToken()).thenReturn(mock(OAuth2AccessToken.class));
+        when(client.getRefreshToken()).thenReturn(mock(OAuth2RefreshToken.class));
+        when(authorizedClientService.loadAuthorizedClient("keycloak", "test-subject"))
+            .thenReturn(client);
+
+        mockMvc.perform(get("/token/boundary").with(oidcLogin()
+                .idToken(token -> token.subject("test-subject"))))
+            .andExpect(status().isOk())
+            .andExpect(header().string("Cache-Control", "no-store"))
+            .andExpect(jsonPath("$.accessTokenStored").value(true))
+            .andExpect(jsonPath("$.refreshTokenStored").value(true))
+            .andExpect(jsonPath("$.browserReceivesRefreshToken").value(false))
+            .andExpect(jsonPath("$.access_token").doesNotExist())
+            .andExpect(jsonPath("$.refresh_token").doesNotExist());
+    }
+
+    @Test
+    void handsOffAccessTokenOnlyAndMarksResponseNoStore() throws Exception {
+        Instant issuedAt = Instant.parse("2026-07-25T00:00:00Z");
+        OAuth2AccessToken accessToken = new OAuth2AccessToken(
+            OAuth2AccessToken.TokenType.BEARER,
+            "test-access-token",
+            issuedAt,
+            issuedAt.plusSeconds(300)
+        );
+        OAuth2AuthorizedClient client = mock(OAuth2AuthorizedClient.class);
+        when(client.getAccessToken()).thenReturn(accessToken);
+        when(authorizedClientManager.authorize(any(OAuth2AuthorizeRequest.class)))
+            .thenReturn(client);
+
+        mockMvc.perform(get("/token/access").with(oidcLogin()
+                .idToken(token -> token.subject("test-subject"))))
+            .andExpect(status().isOk())
+            .andExpect(header().string("Cache-Control", "no-store"))
+            .andExpect(header().string("Pragma", "no-cache"))
+            .andExpect(jsonPath("$.length()").value(3))
+            .andExpect(jsonPath("$.access_token").value("test-access-token"))
+            .andExpect(jsonPath("$.token_type").value("Bearer"))
+            .andExpect(jsonPath("$.expires_at").value("2026-07-25T00:05:00Z"))
+            .andExpect(jsonPath("$.refresh_token").doesNotExist());
+    }
+}