feat(ap2): add confidential token mediator

token-mediator/.dockerignore

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+target/

token-mediator/Dockerfile

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+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

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+<?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

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+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

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+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

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+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

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+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

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+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

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+<!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

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+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());
+    }
+}