feat(ap2): add confidential token mediator

.env.example

@@ -6,5 +6,12 @@ POSTGRES_DB=keycloak
 POSTGRES_USER=keycloak
 POSTGRES_PASSWORD=change-me-postgres-password
 
+# Keycloak resolves these placeholders while importing the realm.
+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
+ADMIN_USER_PASSWORD=change-me-admin-user-password
+REGULAR_USER_PASSWORD=change-me-regular-user-password
+
 # Port 80 is the single-EC2 target. 8088 avoids common local port conflicts.
 NGINX_PORT=8088

.gitignore

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

README.md

@@ -63,3 +63,49 @@ docker compose down -v && docker compose up --build -d
 `start-dev`와 로컬 HTTP 설정은 학습 전용입니다. 운영 환경에서는
 optimized Keycloak image, HTTPS, 엄격한 hostname 및 외부 secret store를
 사용해야 합니다.
+
+## Realm baseline
+
+`keycloak/import/keycloak-patterns-realm.json`은 시작 시 자동 import됩니다.
+하나의 `keycloak-patterns` realm 안에서 패턴마다 client를 분리합니다.
+
+| Client | 유형 | 패턴 |
+|---|---|---|
+| `spa-public` | public + PKCE S256 | AP1 |
+| `token-mediating-confidential` | confidential | AP2 |
+| `bff-confidential` | confidential | AP3 |
+| `edge-proxy` | confidential | AP4 |
+
+confidential client secret과 테스트 사용자 password는 JSON에 평문으로
+저장하지 않습니다. JSON에는 `${ENVIRONMENT_VARIABLE}` placeholder만
+커밋하고, Keycloak 26.7.0이 import 시 `.env` 값을 주입합니다.
+
+```bash
+python3 scripts/validate-realm.py
+docker compose down -v
+docker compose up -d --wait
+./scripts/verify-realm.sh
+```
+
+실행 중인 DB에서 CLI realm export를 재현하려면 다음 명령을 사용합니다.
+Keycloak을 잠시 중지하고 export한 뒤 자동으로 다시 올립니다.
+
+```bash
+./scripts/export-realm.sh
+```
+
+runtime export에는 실제 client secret과 credential hash가 포함될 수 있어
+gitignored `build/keycloak-export/`에 권한 `0600`으로만 저장됩니다.
+
+## AP2: Token-Mediating Backend
+
+`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-pattern2.sh
+```
+
+`/token/boundary`는 실제 token 값을 반환하지 않고 서버 저장 여부만 보여줍니다.

docker-compose.yml

@@ -35,6 +35,11 @@ services:
       KC_HEALTH_ENABLED: "true"
       KC_BOOTSTRAP_ADMIN_USERNAME: ${KC_BOOTSTRAP_ADMIN_USERNAME:?set KC_BOOTSTRAP_ADMIN_USERNAME in .env}
       KC_BOOTSTRAP_ADMIN_PASSWORD: ${KC_BOOTSTRAP_ADMIN_PASSWORD:?set KC_BOOTSTRAP_ADMIN_PASSWORD in .env}
+      TOKEN_MEDIATING_CLIENT_SECRET: ${TOKEN_MEDIATING_CLIENT_SECRET:?set TOKEN_MEDIATING_CLIENT_SECRET in .env}
+      BFF_CLIENT_SECRET: ${BFF_CLIENT_SECRET:?set BFF_CLIENT_SECRET in .env}
+      EDGE_PROXY_CLIENT_SECRET: ${EDGE_PROXY_CLIENT_SECRET:?set EDGE_PROXY_CLIENT_SECRET in .env}
+      ADMIN_USER_PASSWORD: ${ADMIN_USER_PASSWORD:?set ADMIN_USER_PASSWORD in .env}
+      REGULAR_USER_PASSWORD: ${REGULAR_USER_PASSWORD:?set REGULAR_USER_PASSWORD in .env}
     ports:
       - "127.0.0.1:8080:8080"
     volumes:
@@ -81,6 +86,29 @@ services:
       - keycloak-net
     restart: unless-stopped
 
+  token-mediator:
+    build:
+      context: ./token-mediator
+    environment:
+      SERVER_PORT: "8082"
+      KEYCLOAK_CLIENT_SECRET: ${TOKEN_MEDIATING_CLIENT_SECRET:?set TOKEN_MEDIATING_CLIENT_SECRET in .env}
+    ports:
+      - "127.0.0.1:8082:8082"
+    depends_on:
+      keycloak:
+        condition: service_healthy
+    healthcheck:
+      test:
+        - CMD-SHELL
+        - 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:
       context: ./frontend

e2e/package-lock.json

@@ -0,0 +1,28 @@
+{
+  "name": "keycloak-pattern-e2e",
+  "version": "1.0.0",
+  "lockfileVersion": 3,
+  "requires": true,
+  "packages": {
+    "": {
+      "name": "keycloak-pattern-e2e",
+      "version": "1.0.0",
+      "devDependencies": {
+        "playwright-core": "1.62.0"
+      }
+    },
+    "node_modules/playwright-core": {
+      "version": "1.62.0",
+      "resolved": "https://registry.npmjs.org/playwright-core/-/playwright-core-1.62.0.tgz",
+      "integrity": "sha512-nsNRyq0r2zsG8AcRHWknc9QRA5XCueC7gWMrs+Gx2tlZn9hcl8zudfh00lhJPY1DE7NmZ6bDsT9g2yey8mXljA==",
+      "dev": true,
+      "license": "Apache-2.0",
+      "bin": {
+        "playwright-core": "cli.js"
+      },
+      "engines": {
+        "node": ">=20"
+      }
+    }
+  }
+}

e2e/package.json

@@ -0,0 +1,12 @@
+{
+  "name": "keycloak-pattern-e2e",
+  "private": true,
+  "version": "1.0.0",
+  "type": "module",
+  "scripts": {
+    "test:pattern2": "node pattern2.mjs"
+  },
+  "devDependencies": {
+    "playwright-core": "1.62.0"
+  }
+}

e2e/pattern2.mjs

@@ -0,0 +1,57 @@
+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");
+
+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 page.locator("#username").fill(
+    process.env.E2E_USERNAME ?? "regular-user",
+  );
+  await page.locator("#password").fill(password);
+  await page.locator("#kc-login").click();
+  await page.waitForURL("http://localhost:8082/");
+
+  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 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);
+
+  console.log(
+    "pattern2 confidential client verified: server code exchange, server access/refresh custody, HttpOnly session",
+  );
+} finally {
+  await browser.close();
+}

keycloak/import/keycloak-patterns-realm.json

@@ -0,0 +1,165 @@
+{
+  "realm": "keycloak-patterns",
+  "displayName": "Keycloak Authentication Patterns",
+  "enabled": true,
+  "sslRequired": "external",
+  "registrationAllowed": false,
+  "resetPasswordAllowed": false,
+  "editUsernameAllowed": false,
+  "loginWithEmailAllowed": true,
+  "duplicateEmailsAllowed": false,
+  "bruteForceProtected": true,
+  "accessTokenLifespan": 300,
+  "ssoSessionIdleTimeout": 1800,
+  "ssoSessionMaxLifespan": 36000,
+  "offlineSessionIdleTimeout": 2592000,
+  "revokeRefreshToken": true,
+  "refreshTokenMaxReuse": 0,
+  "roles": {
+    "realm": [
+      {
+        "name": "admin-role",
+        "description": "Administrative role used by authorization examples"
+      },
+      {
+        "name": "user-role",
+        "description": "Regular authenticated user role"
+      }
+    ]
+  },
+  "clients": [
+    {
+      "clientId": "spa-public",
+      "name": "AP1 SPA Public Client",
+      "description": "Browser-based OAuth client using Authorization Code and PKCE",
+      "enabled": true,
+      "protocol": "openid-connect",
+      "publicClient": true,
+      "standardFlowEnabled": true,
+      "implicitFlowEnabled": false,
+      "directAccessGrantsEnabled": false,
+      "serviceAccountsEnabled": false,
+      "frontchannelLogout": true,
+      "redirectUris": [
+        "http://localhost:8088/*",
+        "http://127.0.0.1:8088/*"
+      ],
+      "webOrigins": [
+        "http://localhost:8088",
+        "http://127.0.0.1:8088"
+      ],
+      "attributes": {
+        "pkce.code.challenge.method": "S256",
+        "post.logout.redirect.uris": "http://localhost:8088/*##http://127.0.0.1:8088/*"
+      }
+    },
+    {
+      "clientId": "token-mediating-confidential",
+      "name": "AP2 Token-Mediating Backend",
+      "description": "Confidential backend that keeps refresh tokens server-side",
+      "enabled": true,
+      "protocol": "openid-connect",
+      "publicClient": false,
+      "clientAuthenticatorType": "client-secret",
+      "secret": "${TOKEN_MEDIATING_CLIENT_SECRET}",
+      "standardFlowEnabled": true,
+      "implicitFlowEnabled": false,
+      "directAccessGrantsEnabled": false,
+      "serviceAccountsEnabled": false,
+      "frontchannelLogout": true,
+      "redirectUris": [
+        "http://localhost:8082/login/oauth2/code/keycloak"
+      ],
+      "webOrigins": [
+        "http://localhost:8082"
+      ],
+      "attributes": {
+        "post.logout.redirect.uris": "http://localhost:8082/*"
+      }
+    },
+    {
+      "clientId": "bff-confidential",
+      "name": "AP3 Backend-for-Frontend",
+      "description": "Confidential BFF that keeps all OAuth tokens server-side",
+      "enabled": true,
+      "protocol": "openid-connect",
+      "publicClient": false,
+      "clientAuthenticatorType": "client-secret",
+      "secret": "${BFF_CLIENT_SECRET}",
+      "standardFlowEnabled": true,
+      "implicitFlowEnabled": false,
+      "directAccessGrantsEnabled": false,
+      "serviceAccountsEnabled": false,
+      "frontchannelLogout": true,
+      "redirectUris": [
+        "http://localhost:8083/login/oauth2/code/keycloak"
+      ],
+      "webOrigins": [
+        "http://localhost:8083"
+      ],
+      "attributes": {
+        "post.logout.redirect.uris": "http://localhost:8083/*"
+      }
+    },
+    {
+      "clientId": "edge-proxy",
+      "name": "AP4 Edge Forward Auth",
+      "description": "Confidential oauth2-proxy OIDC client",
+      "enabled": true,
+      "protocol": "openid-connect",
+      "publicClient": false,
+      "clientAuthenticatorType": "client-secret",
+      "secret": "${EDGE_PROXY_CLIENT_SECRET}",
+      "standardFlowEnabled": true,
+      "implicitFlowEnabled": false,
+      "directAccessGrantsEnabled": false,
+      "serviceAccountsEnabled": false,
+      "frontchannelLogout": true,
+      "redirectUris": [
+        "http://localhost:4180/oauth2/callback"
+      ],
+      "webOrigins": [],
+      "attributes": {
+        "post.logout.redirect.uris": "http://localhost:8088/*"
+      }
+    }
+  ],
+  "users": [
+    {
+      "username": "admin-user",
+      "enabled": true,
+      "email": "admin-user@example.test",
+      "emailVerified": true,
+      "firstName": "Admin",
+      "lastName": "User",
+      "realmRoles": [
+        "admin-role"
+      ],
+      "credentials": [
+        {
+          "type": "password",
+          "value": "${ADMIN_USER_PASSWORD}",
+          "temporary": false
+        }
+      ]
+    },
+    {
+      "username": "regular-user",
+      "enabled": true,
+      "email": "regular-user@example.test",
+      "emailVerified": true,
+      "firstName": "Regular",
+      "lastName": "User",
+      "realmRoles": [
+        "user-role"
+      ],
+      "credentials": [
+        {
+          "type": "password",
+          "value": "${REGULAR_USER_PASSWORD}",
+          "temporary": false
+        }
+      ]
+    }
+  ]
+}

scripts/export-realm.sh

@@ -0,0 +1,30 @@
+#!/usr/bin/env sh
+set -eu
+
+compose_file=${COMPOSE_FILE:-docker-compose.yml}
+output_dir=${REALM_EXPORT_DIR:-"$(pwd)/build/keycloak-export"}
+output_file="$output_dir/keycloak-patterns-realm.json"
+
+mkdir -p "$output_dir"
+
+restart_keycloak() {
+  trap - EXIT INT TERM
+  docker compose -f "$compose_file" up -d --wait >/dev/null
+}
+trap restart_keycloak EXIT
+trap 'exit 130' INT
+trap 'exit 143' TERM
+
+docker compose -f "$compose_file" stop keycloak >/dev/null
+docker compose -f "$compose_file" run --rm --no-deps \
+  --volume "$output_dir:/opt/keycloak/data/export" \
+  keycloak \
+    export \
+    --realm keycloak-patterns \
+    --file /opt/keycloak/data/export/keycloak-patterns-realm.json \
+    --users same_file
+
+chmod 600 "$output_file"
+python3 scripts/validate-realm.py --runtime "$output_file"
+
+echo "runtime realm export written to $output_file"

scripts/validate-realm.py

@@ -0,0 +1,118 @@
+#!/usr/bin/env python3
+"""Validate the committed realm template or a runtime Keycloak CLI export."""
+
+from __future__ import annotations
+
+import argparse
+import json
+from pathlib import Path
+from typing import Any
+
+REALM_NAME = "keycloak-patterns"
+PUBLIC_CLIENT = "spa-public"
+CONFIDENTIAL_CLIENTS = {
+    "token-mediating-confidential": "${TOKEN_MEDIATING_CLIENT_SECRET}",
+    "bff-confidential": "${BFF_CLIENT_SECRET}",
+    "edge-proxy": "${EDGE_PROXY_CLIENT_SECRET}",
+}
+EXPECTED_ROLES = {"admin-role", "user-role"}
+EXPECTED_USERS = {"admin-user", "regular-user"}
+
+
+def parse_args() -> argparse.Namespace:
+    parser = argparse.ArgumentParser()
+    parser.add_argument(
+        "realm_file",
+        nargs="?",
+        type=Path,
+        default=Path("keycloak/import/keycloak-patterns-realm.json"),
+    )
+    parser.add_argument(
+        "--runtime",
+        action="store_true",
+        help="validate an expanded CLI export instead of the committed template",
+    )
+    return parser.parse_args()
+
+
+def require(condition: bool, message: str) -> None:
+    if not condition:
+        raise SystemExit(f"realm validation failed: {message}")
+
+
+def indexed(items: list[dict[str, Any]], key: str) -> dict[str, dict[str, Any]]:
+    return {str(item[key]): item for item in items}
+
+
+def validate(path: Path, runtime: bool) -> None:
+    document = json.loads(path.read_text(encoding="utf-8"))
+    require(document.get("realm") == REALM_NAME, f"realm must be {REALM_NAME}")
+    require(document.get("enabled") is True, "realm must be enabled")
+    require(document.get("accessTokenLifespan") == 300, "access token TTL must be 300s")
+    require(document.get("revokeRefreshToken") is True, "refresh token rotation must be enabled")
+    require(document.get("refreshTokenMaxReuse") == 0, "refresh token max reuse must be 0")
+
+    clients = indexed(document.get("clients", []), "clientId")
+    expected_client_ids = {PUBLIC_CLIENT, *CONFIDENTIAL_CLIENTS}
+    require(expected_client_ids <= clients.keys(), "all four pattern clients must exist")
+    if not runtime:
+        require(clients.keys() == expected_client_ids, "template must declare exactly four clients")
+
+    spa = clients[PUBLIC_CLIENT]
+    require(spa.get("publicClient") is True, "spa-public must be a public client")
+    require("secret" not in spa, "spa-public must not have a client secret")
+    require(spa.get("standardFlowEnabled") is True, "spa-public standard flow must be enabled")
+    require(
+        spa.get("directAccessGrantsEnabled") is False,
+        "spa-public direct access grants must be disabled",
+    )
+    require(
+        spa.get("attributes", {}).get("pkce.code.challenge.method") == "S256",
+        "spa-public must enforce PKCE S256",
+    )
+
+    for client_id, placeholder in CONFIDENTIAL_CLIENTS.items():
+        client = clients[client_id]
+        require(client.get("publicClient") is False, f"{client_id} must be confidential")
+        require(
+            client.get("clientAuthenticatorType") == "client-secret",
+            f"{client_id} must use client-secret authentication",
+        )
+        secret = client.get("secret")
+        if runtime:
+            require(isinstance(secret, str) and len(secret) >= 16, f"{client_id} secret missing")
+            require(not secret.startswith("${"), f"{client_id} placeholder was not resolved")
+        else:
+            require(secret == placeholder, f"{client_id} must use an env placeholder")
+
+    roles = {
+        role["name"]
+        for role in document.get("roles", {}).get("realm", [])
+        if "name" in role
+    }
+    require(EXPECTED_ROLES <= roles, "admin-role and user-role must exist")
+
+    users = indexed(document.get("users", []), "username")
+    require(EXPECTED_USERS <= users.keys(), "both baseline users must exist")
+    if not runtime:
+        expected_passwords = {
+            "admin-user": "${ADMIN_USER_PASSWORD}",
+            "regular-user": "${REGULAR_USER_PASSWORD}",
+        }
+        for username, placeholder in expected_passwords.items():
+            credentials = users[username].get("credentials", [])
+            require(len(credentials) == 1, f"{username} must have one initial credential")
+            require(
+                credentials[0].get("value") == placeholder,
+                f"{username} password must use an env placeholder",
+            )
+
+    print(
+        f"realm validated: {REALM_NAME}, four pattern clients, "
+        f"{len(EXPECTED_ROLES)} roles, {len(EXPECTED_USERS)} users"
+    )
+
+
+if __name__ == "__main__":
+    arguments = parse_args()
+    validate(arguments.realm_file, arguments.runtime)

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"

scripts/verify-realm.sh

@@ -0,0 +1,39 @@
+#!/usr/bin/env sh
+set -eu
+
+compose_file=${COMPOSE_FILE:-docker-compose.yml}
+
+python3 scripts/validate-realm.py
+./scripts/verify-stack.sh
+
+curl --fail --silent --show-error --output /dev/null \
+  "http://localhost:8080/realms/keycloak-patterns/.well-known/openid-configuration"
+
+docker compose -f "$compose_file" exec -T keycloak sh -ec '
+  kcadm=/opt/keycloak/bin/kcadm.sh
+  "$kcadm" config credentials \
+    --server http://localhost:8080 \
+    --realm master \
+    --user "$KC_BOOTSTRAP_ADMIN_USERNAME" \
+    --password "$KC_BOOTSTRAP_ADMIN_PASSWORD" >/dev/null
+
+  clients=$("$kcadm" get clients -r keycloak-patterns --fields clientId)
+  for client in \
+    spa-public \
+    token-mediating-confidential \
+    bff-confidential \
+    edge-proxy
+  do
+    printf "%s" "$clients" | grep -q "\"$client\""
+  done
+
+  users=$("$kcadm" get users -r keycloak-patterns --fields username)
+  printf "%s" "$users" | grep -q "\"admin-user\""
+  printf "%s" "$users" | grep -q "\"regular-user\""
+
+  roles=$("$kcadm" get roles -r keycloak-patterns --fields name)
+  printf "%s" "$roles" | grep -q "\"admin-role\""
+  printf "%s" "$roles" | grep -q "\"user-role\""
+'
+
+echo "realm verified: import, discovery, four clients, two roles, two users"

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/SecurityConfig.java

@@ -0,0 +1,29 @@
+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.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();
+    }
+}

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 +1,20 @@
+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());
+});

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

@@ -0,0 +1,29 @@
+<!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>
+    <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 +1,50 @@
+package com.example.keycloakpattern.mediator;
+
+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 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.OAuth2AuthorizedClient;
+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;
+
+    @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());
+    }
+}