feat(ap3): add CSRF and SameSite defenses

.gitignore

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

README.md

@@ -96,3 +96,19 @@ 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.
+
+## AP3: Backend-for-Frontend
+
+`develop-keycloak-pattern3`의 Spring BFF는 `http://localhost:8083`에서
+실행됩니다. 브라우저에는 HttpOnly session cookie만 두고 access/refresh
+token은 BFF가 서버에 보관합니다. `/bff/api/me`는 BFF가 보유 access
+token을 붙여 Resource Server로 proxy합니다.
+
+```bash
+./scripts/verify-pattern3.sh
+```
+
+자세한 경계와 session 저장소 trade-off는
+[`docs/ap3-bff-boundary.md`](docs/ap3-bff-boundary.md)를 참고하세요.
+최종 AP3 branch는 `AP3_SESSION; HttpOnly; SameSite=Lax`와 Spring CSRF
+token을 함께 사용하며, token 없는 상태 변경 요청은 403으로 거부합니다.

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

@@ -0,0 +1,29 @@
+package com.example.keycloakpattern;
+
+import org.springframework.security.oauth2.core.OAuth2Error;
+import org.springframework.security.oauth2.core.OAuth2TokenValidator;
+import org.springframework.security.oauth2.core.OAuth2TokenValidatorResult;
+import org.springframework.security.oauth2.jwt.Jwt;
+
+final class AudienceValidator implements OAuth2TokenValidator<Jwt> {
+
+    private static final OAuth2Error MISSING_AUDIENCE = new OAuth2Error(
+        "invalid_token",
+        "The required resource audience is missing",
+        null
+    );
+
+    private final String expectedAudience;
+
+    AudienceValidator(String expectedAudience) {
+        this.expectedAudience = expectedAudience;
+    }
+
+    @Override
+    public OAuth2TokenValidatorResult validate(Jwt jwt) {
+        if (jwt.getAudience().contains(expectedAudience)) {
+            return OAuth2TokenValidatorResult.success();
+        }
+        return OAuth2TokenValidatorResult.failure(MISSING_AUDIENCE);
+    }
+}

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

@@ -0,0 +1,31 @@
+package com.example.keycloakpattern;
+
+import org.springframework.beans.factory.annotation.Value;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.security.oauth2.core.DelegatingOAuth2TokenValidator;
+import org.springframework.security.oauth2.core.OAuth2TokenValidator;
+import org.springframework.security.oauth2.jwt.Jwt;
+import org.springframework.security.oauth2.jwt.JwtDecoder;
+import org.springframework.security.oauth2.jwt.JwtValidators;
+import org.springframework.security.oauth2.jwt.NimbusJwtDecoder;
+
+@Configuration
+public class JwtDecoderConfig {
+
+    @Bean
+    JwtDecoder jwtDecoder(
+        @Value("${spring.security.oauth2.resourceserver.jwt.issuer-uri}") String issuer,
+        @Value("${spring.security.oauth2.resourceserver.jwt.jwk-set-uri}") String jwkSetUri,
+        @Value("${security.expected-audience}") String expectedAudience
+    ) {
+        NimbusJwtDecoder decoder = NimbusJwtDecoder.withJwkSetUri(jwkSetUri).build();
+        OAuth2TokenValidator<Jwt> issuerAndTimestamp =
+            JwtValidators.createDefaultWithIssuer(issuer);
+        OAuth2TokenValidator<Jwt> audience = new AudienceValidator(expectedAudience);
+        decoder.setJwtValidator(
+            new DelegatingOAuth2TokenValidator<>(issuerAndTimestamp, audience)
+        );
+        return decoder;
+    }
+}

backend/src/main/resources/application.yml

@@ -11,6 +11,9 @@ spring:
           issuer-uri: ${SPRING_SECURITY_OAUTH2_RESOURCESERVER_JWT_ISSUER_URI:http://localhost:8080/realms/keycloak-patterns}
           jwk-set-uri: ${SPRING_SECURITY_OAUTH2_RESOURCESERVER_JWT_JWK_SET_URI:http://localhost:8080/realms/keycloak-patterns/protocol/openid-connect/certs}
 
+security:
+  expected-audience: ${SECURITY_EXPECTED_AUDIENCE:keycloak-pattern-api}
+
 management:
   endpoint:
     health:

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

@@ -0,0 +1,49 @@
+package com.example.keycloakpattern;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import java.time.Instant;
+import java.util.List;
+import java.util.Map;
+
+import org.junit.jupiter.api.Test;
+import org.springframework.security.oauth2.core.OAuth2TokenValidatorResult;
+import org.springframework.security.oauth2.jwt.Jwt;
+
+class AudienceValidatorTest {
+
+    private final AudienceValidator validator =
+        new AudienceValidator("keycloak-pattern-api");
+
+    @Test
+    void acceptsRequiredAudience() {
+        OAuth2TokenValidatorResult result = validator.validate(jwtWithAudience(
+            List.of("account", "keycloak-pattern-api")
+        ));
+
+        assertThat(result.hasErrors()).isFalse();
+    }
+
+    @Test
+    void rejectsForeignAudience() {
+        OAuth2TokenValidatorResult result = validator.validate(jwtWithAudience(
+            List.of("another-resource")
+        ));
+
+        assertThat(result.hasErrors()).isTrue();
+        assertThat(result.getErrors())
+            .extracting(error -> error.getErrorCode())
+            .containsExactly("invalid_token");
+    }
+
+    private Jwt jwtWithAudience(List<String> audience) {
+        Instant now = Instant.now();
+        return new Jwt(
+            "test-token",
+            now,
+            now.plusSeconds(300),
+            Map.of("alg", "none"),
+            Map.of("sub", "test-subject", "aud", audience)
+        );
+    }
+}

bff/.dockerignore

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

bff/Dockerfile

@@ -0,0 +1,14 @@
+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-bff.jar app.jar
+USER spring:spring
+EXPOSE 8083
+ENTRYPOINT ["java", "-jar", "/app/app.jar"]

bff/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-bff</artifactId>
+    <version>0.0.1-SNAPSHOT</version>
+    <name>keycloak-bff</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-bff</finalName>
+        <plugins>
+            <plugin>
+                <groupId>org.springframework.boot</groupId>
+                <artifactId>spring-boot-maven-plugin</artifactId>
+            </plugin>
+        </plugins>
+    </build>
+</project>

bff/src/main/java/com/example/keycloakpattern/bff/BffApplication.java

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

bff/src/main/java/com/example/keycloakpattern/bff/BffController.java

@@ -0,0 +1,112 @@
+package com.example.keycloakpattern.bff;
+
+import java.util.LinkedHashMap;
+import java.util.Map;
+import java.util.concurrent.atomic.AtomicReference;
+
+import org.springframework.beans.factory.annotation.Value;
+import org.springframework.http.CacheControl;
+import org.springframework.http.HttpHeaders;
+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.client.OAuth2AuthorizedClientService;
+import org.springframework.web.bind.annotation.GetMapping;
+import org.springframework.web.bind.annotation.PostMapping;
+import org.springframework.web.bind.annotation.RequestParam;
+import org.springframework.web.bind.annotation.RestController;
+import org.springframework.web.client.RestClient;
+import org.springframework.web.server.ResponseStatusException;
+
+import static org.springframework.http.HttpStatus.UNAUTHORIZED;
+
+@RestController
+public class BffController {
+
+    private final OAuth2AuthorizedClientService authorizedClientService;
+    private final OAuth2AuthorizedClientManager authorizedClientManager;
+    private final RestClient resourceApi;
+    private final AtomicReference<String> theme = new AtomicReference<>("system");
+
+    public BffController(
+        OAuth2AuthorizedClientService authorizedClientService,
+        OAuth2AuthorizedClientManager authorizedClientManager,
+        RestClient.Builder restClientBuilder,
+        @Value("${resource-api.base-url}") String resourceApiBaseUrl
+    ) {
+        this.authorizedClientService = authorizedClientService;
+        this.authorizedClientManager = authorizedClientManager;
+        this.resourceApi = restClientBuilder.baseUrl(resourceApiBaseUrl).build();
+    }
+
+    @GetMapping("/bff/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", "AP3-backend-for-frontend");
+        response.put("principal", authentication.getName());
+        response.put("accessTokenStoredOnServer", client != null
+            && client.getAccessToken() != null);
+        response.put("refreshTokenStoredOnServer", client != null
+            && client.getRefreshToken() != null);
+        response.put("browserTokenCount", 0);
+        response.put("csrfProtectionEnabled", true);
+
+        return ResponseEntity.ok()
+            .cacheControl(CacheControl.noStore())
+            .header("Pragma", "no-cache")
+            .body(response);
+    }
+
+    @GetMapping("/bff/api/me")
+    ResponseEntity<?> currentUser(Authentication authentication) {
+        OAuth2AuthorizedClient client = authorizedClient(authentication);
+        return resourceApi.get()
+            .uri("/api/me")
+            .header(
+                HttpHeaders.AUTHORIZATION,
+                "Bearer " + client.getAccessToken().getTokenValue()
+            )
+            .retrieve()
+            .toEntity(Map.class);
+    }
+
+    @PostMapping("/bff/api/preferences")
+    Map<String, Object> updatePreference(
+        Authentication authentication,
+        @RequestParam(defaultValue = "system") String theme
+    ) {
+        this.theme.set(theme);
+        return Map.of(
+            "updated", true,
+            "theme", this.theme.get(),
+            "principal", authentication.getName()
+        );
+    }
+
+    @GetMapping("/bff/api/preferences")
+    Map<String, String> preference() {
+        return Map.of("theme", theme.get());
+    }
+
+    private OAuth2AuthorizedClient authorizedClient(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"
+            );
+        }
+        return client;
+    }
+}

bff/src/main/java/com/example/keycloakpattern/bff/CsrfController.java

@@ -0,0 +1,25 @@
+package com.example.keycloakpattern.bff;
+
+import java.util.Map;
+
+import org.springframework.http.CacheControl;
+import org.springframework.http.ResponseEntity;
+import org.springframework.security.web.csrf.CsrfToken;
+import org.springframework.web.bind.annotation.GetMapping;
+import org.springframework.web.bind.annotation.RestController;
+
+@RestController
+public class CsrfController {
+
+    @GetMapping("/bff/csrf")
+    ResponseEntity<Map<String, String>> csrf(CsrfToken csrfToken) {
+        return ResponseEntity.ok()
+            .cacheControl(CacheControl.noStore())
+            .header("Pragma", "no-cache")
+            .body(Map.of(
+                "headerName", csrfToken.getHeaderName(),
+                "parameterName", csrfToken.getParameterName(),
+                "token", csrfToken.getToken()
+            ));
+    }
+}

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

@@ -0,0 +1,80 @@
+package com.example.keycloakpattern.bff;
+
+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.oauth2.client.web.DefaultOAuth2AuthorizationRequestResolver;
+import org.springframework.security.oauth2.client.web.OAuth2AuthorizationRequestCustomizers;
+import org.springframework.security.web.SecurityFilterChain;
+import org.springframework.security.web.csrf.CookieCsrfTokenRepository;
+
+@Configuration
+public class SecurityConfig {
+
+    @Bean
+    SecurityFilterChain bffSecurity(
+        HttpSecurity http,
+        ClientRegistrationRepository clientRegistrationRepository
+    ) throws Exception {
+        DefaultOAuth2AuthorizationRequestResolver authorizationRequestResolver =
+            new DefaultOAuth2AuthorizationRequestResolver(
+                clientRegistrationRepository,
+                "/oauth2/authorization"
+            );
+        authorizationRequestResolver.setAuthorizationRequestCustomizer(
+            OAuth2AuthorizationRequestCustomizers.withPkce()
+        );
+
+        CookieCsrfTokenRepository csrfTokenRepository =
+            CookieCsrfTokenRepository.withHttpOnlyFalse();
+        csrfTokenRepository.setCookiePath("/");
+
+        return http
+            .csrf(csrf -> csrf
+                .csrfTokenRepository(csrfTokenRepository)
+                .csrfTokenRequestHandler(new SpaCsrfTokenRequestHandler()))
+            .authorizeHttpRequests(authorize -> authorize
+                .requestMatchers(
+                    "/",
+                    "/index.html",
+                    "/app.js",
+                    "/favicon.ico",
+                    "/actuator/health",
+                    "/actuator/health/**"
+                )
+                .permitAll()
+                .anyRequest()
+                .authenticated())
+            .oauth2Login(oauth2 -> oauth2
+                .authorizationEndpoint(endpoint -> endpoint
+                    .authorizationRequestResolver(authorizationRequestResolver))
+                .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;
+    }
+}

bff/src/main/java/com/example/keycloakpattern/bff/SpaCsrfTokenRequestHandler.java

@@ -0,0 +1,40 @@
+package com.example.keycloakpattern.bff;
+
+import java.util.function.Supplier;
+
+import jakarta.servlet.http.HttpServletRequest;
+import jakarta.servlet.http.HttpServletResponse;
+
+import org.springframework.security.web.csrf.CsrfToken;
+import org.springframework.security.web.csrf.CsrfTokenRequestAttributeHandler;
+import org.springframework.security.web.csrf.CsrfTokenRequestHandler;
+import org.springframework.security.web.csrf.XorCsrfTokenRequestAttributeHandler;
+import org.springframework.util.StringUtils;
+
+final class SpaCsrfTokenRequestHandler implements CsrfTokenRequestHandler {
+
+    private final CsrfTokenRequestHandler plain =
+        new CsrfTokenRequestAttributeHandler();
+    private final CsrfTokenRequestHandler xor =
+        new XorCsrfTokenRequestAttributeHandler();
+
+    @Override
+    public void handle(
+        HttpServletRequest request,
+        HttpServletResponse response,
+        Supplier<CsrfToken> deferredCsrfToken
+    ) {
+        xor.handle(request, response, deferredCsrfToken);
+    }
+
+    @Override
+    public String resolveCsrfTokenValue(
+        HttpServletRequest request,
+        CsrfToken csrfToken
+    ) {
+        if (StringUtils.hasText(request.getHeader(csrfToken.getHeaderName()))) {
+            return plain.resolveCsrfTokenValue(request, csrfToken);
+        }
+        return xor.resolveCsrfTokenValue(request, csrfToken);
+    }
+}

bff/src/main/resources/application.yml

@@ -0,0 +1,47 @@
+server:
+  port: ${SERVER_PORT:8083}
+  servlet:
+    session:
+      cookie:
+        name: AP3_SESSION
+        http-only: true
+        same-site: lax
+
+spring:
+  application:
+    name: keycloak-bff
+  security:
+    oauth2:
+      client:
+        registration:
+          keycloak:
+            provider: keycloak
+            client-id: bff-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
+
+resource-api:
+  base-url: ${RESOURCE_API_BASE_URL:http://localhost:8081}
+
+management:
+  endpoint:
+    health:
+      probes:
+        enabled: true
+  endpoints:
+    web:
+      exposure:
+        include: health,info

bff/src/main/resources/static/app.js

@@ -0,0 +1,59 @@
+const result = document.querySelector("#result");
+
+function render(value) {
+  result.textContent = JSON.stringify(value, null, 2);
+}
+
+function readCookie(name) {
+  const prefix = `${encodeURIComponent(name)}=`;
+  const value = document.cookie
+    .split("; ")
+    .find((cookie) => cookie.startsWith(prefix));
+  return value ? decodeURIComponent(value.slice(prefix.length)) : null;
+}
+
+async function request(path, options = {}) {
+  const response = await fetch(path, {
+    ...options,
+    headers: { Accept: "application/json", ...options.headers },
+  });
+  if (response.redirected || response.status === 401) {
+    window.location.assign("/oauth2/authorization/keycloak");
+    return null;
+  }
+  const body = await response.json();
+  render({ status: response.status, ...body });
+  return { response, body };
+}
+
+document.querySelector("#login").addEventListener("click", () => {
+  window.location.assign("/oauth2/authorization/keycloak");
+});
+
+document.querySelector("#inspect").addEventListener("click", () => {
+  void request("/bff/token-boundary");
+});
+
+document.querySelector("#call-bff").addEventListener("click", () => {
+  void request("/bff/api/me");
+});
+
+document.querySelector("#change-with-csrf").addEventListener("click", async () => {
+  const csrfResponse = await fetch("/bff/csrf", {
+    headers: { Accept: "application/json" },
+  });
+  const csrf = await csrfResponse.json();
+  const csrfToken = readCookie("XSRF-TOKEN");
+  if (!csrfToken) {
+    render({ status: 500, error: "XSRF-TOKEN cookie was not created" });
+    return;
+  }
+  await request("/bff/api/preferences", {
+    method: "POST",
+    body: new URLSearchParams({ theme: "dark" }),
+    headers: {
+      "Content-Type": "application/x-www-form-urlencoded",
+      [csrf.headerName]: csrfToken,
+    },
+  });
+});

bff/src/main/resources/static/index.html

@@ -0,0 +1,31 @@
+<!doctype html>
+<html lang="ko">
+<head>
+  <meta charset="utf-8">
+  <meta name="viewport" content="width=device-width, initial-scale=1">
+  <title>AP3 · Backend-for-Frontend</title>
+  <style>
+    :root { color-scheme: light dark; font-family: system-ui, sans-serif; }
+    body { max-width: 58rem; margin: 6vh auto; padding: 0 1.5rem; line-height: 1.6; }
+    button { margin: 0 0.5rem 0.5rem 0; padding: 0.6rem 0.9rem; cursor: pointer; }
+    pre { min-height: 9rem; padding: 1rem; border-radius: 0.4rem;
+      background: color-mix(in srgb, CanvasText 9%, Canvas); white-space: pre-wrap; }
+  </style>
+</head>
+<body>
+  <main>
+    <h1>AP3 · Backend-for-Frontend</h1>
+    <p>
+      브라우저에는 OAuth token이 전혀 전달되지 않습니다. HttpOnly session
+      cookie로 BFF만 호출하고, BFF가 서버 보관 access token을 Resource
+      Server 요청에 붙입니다.
+    </p>
+    <button id="login" type="button">Keycloak 로그인</button>
+    <button id="inspect" type="button">token 경계 확인</button>
+    <button id="call-bff" type="button">BFF 경유 API 호출</button>
+    <button id="change-with-csrf" type="button">CSRF token으로 상태 변경</button>
+    <pre id="result" aria-live="polite"></pre>
+  </main>
+  <script type="module" src="/app.js"></script>
+</body>
+</html>

bff/src/test/java/com/example/keycloakpattern/bff/BffControllerTest.java

@@ -0,0 +1,90 @@
+package com.example.keycloakpattern.bff;
+
+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.security.test.web.servlet.request.SecurityMockMvcRequestPostProcessors.csrf;
+import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.get;
+import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.post;
+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.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",
+    "resource-api.base-url=http://127.0.0.1:9"
+})
+@AutoConfigureMockMvc
+class BffControllerTest {
+
+    @Autowired
+    private MockMvc mockMvc;
+
+    @MockitoBean
+    private OAuth2AuthorizedClientService authorizedClientService;
+
+    @MockitoBean
+    private OAuth2AuthorizedClientManager authorizedClientManager;
+
+    @Test
+    void reportsServerTokenCustodyWithoutReturningTokens() 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("/bff/token-boundary").with(oidcLogin()
+                .idToken(token -> token.subject("test-subject"))))
+            .andExpect(status().isOk())
+            .andExpect(header().string("Cache-Control", "no-store"))
+            .andExpect(jsonPath("$.accessTokenStoredOnServer").value(true))
+            .andExpect(jsonPath("$.refreshTokenStoredOnServer").value(true))
+            .andExpect(jsonPath("$.browserTokenCount").value(0))
+            .andExpect(jsonPath("$.csrfProtectionEnabled").value(true))
+            .andExpect(jsonPath("$.access_token").doesNotExist())
+            .andExpect(jsonPath("$.refresh_token").doesNotExist());
+    }
+
+    @Test
+    void rejectsStateChangeWithoutCsrfToken() throws Exception {
+        mockMvc.perform(post("/bff/api/preferences")
+                .param("theme", "attacker")
+                .with(oidcLogin().idToken(token -> token.subject("test-subject"))))
+            .andExpect(status().isForbidden());
+    }
+
+    @Test
+    void acceptsStateChangeWithCsrfToken() throws Exception {
+        mockMvc.perform(post("/bff/api/preferences")
+                .param("theme", "dark")
+                .with(oidcLogin().idToken(token -> token.subject("test-subject")))
+                .with(csrf()))
+            .andExpect(status().isOk())
+            .andExpect(jsonPath("$.updated").value(true))
+            .andExpect(jsonPath("$.theme").value("dark"));
+    }
+
+    @Test
+    void exposesSpaCsrfTokenWithoutCaching() throws Exception {
+        mockMvc.perform(get("/bff/csrf").with(oidcLogin()
+                .idToken(token -> token.subject("test-subject"))))
+            .andExpect(status().isOk())
+            .andExpect(header().string("Cache-Control", "no-store"))
+            .andExpect(header().exists("Set-Cookie"))
+            .andExpect(jsonPath("$.headerName").value("X-XSRF-TOKEN"))
+            .andExpect(jsonPath("$.token").isNotEmpty());
+    }
+}

docker-compose.yml

@@ -86,6 +86,32 @@ services:
       - keycloak-net
     restart: unless-stopped
 
+  bff:
+    build:
+      context: ./bff
+    environment:
+      SERVER_PORT: "8083"
+      KEYCLOAK_CLIENT_SECRET: ${BFF_CLIENT_SECRET:?set BFF_CLIENT_SECRET in .env}
+      RESOURCE_API_BASE_URL: http://app:8081
+    ports:
+      - "127.0.0.1:8083:8083"
+    depends_on:
+      keycloak:
+        condition: service_healthy
+      app:
+        condition: service_healthy
+    healthcheck:
+      test:
+        - CMD-SHELL
+        - wget -q -O - http://127.0.0.1:8083/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

docs/ap3-bff-boundary.md

@@ -0,0 +1,36 @@
+# AP3 · Backend-for-Frontend
+
+## 요청과 token 경계
+
+1. 브라우저는 BFF의 `/oauth2/authorization/keycloak`로 로그인을 시작합니다.
+2. Spring `oauth2Login`은 PKCE S256 authorization code flow를 수행합니다.
+3. BFF가 client secret으로 code를 교환하고 access/refresh token을 서버의
+   `OAuth2AuthorizedClientService`에 보관합니다.
+4. 브라우저에는 OAuth token 대신 HttpOnly `AP3_SESSION` 식별자만 남습니다.
+5. 브라우저가 `/bff/api/me`를 cookie로 호출하면 BFF가 access token을
+   `Authorization: Bearer`로 붙여 Resource Server에 fan-out합니다.
+
+Resource Server는 `aud=keycloak-pattern-api`를 검증합니다. 브라우저에서는
+8081로 직접 요청하거나 Keycloak token endpoint를 호출하지 않습니다.
+
+학습용 구성은 단일 인스턴스 메모리에 session과 authorized client를
+보관합니다. BFF를 재시작하면 세션이 사라집니다. 다중 인스턴스 운영에서는
+Spring Session/Redis 같은 공유 저장소와 저장 token 암호화 정책이 필요합니다.
+
+## CSRF와 SameSite 방어
+
+`feature/keycloak-bff-oauth2login-session`에서는 방어 전 비교를 위해
+CSRF를 끄고, 다른 origin의 자동 제출 form이 `/bff/api/preferences`
+상태를 바꾸는 것을 재현합니다.
+
+`feature/keycloak-bff-csrf-samesite-defense`에서는 다음 방어를 함께
+적용합니다.
+
+- Spring synchronizer CSRF token과 `CookieCsrfTokenRepository`
+- JS가 읽는 `XSRF-TOKEN`과 요청의 `X-XSRF-TOKEN` header
+- HttpOnly `AP3_SESSION` cookie의 명시적 `SameSite=Lax`
+
+E2E는 token 없는 동일 위조 POST가 403이 되는 것, CSRF header가 있는
+정상 POST는 200인 것, cross-site POST에는 AP3 session cookie가 제외되는
+것을 각각 확인합니다. SameSite는 CSRF token을 대체하지 않는
+defense-in-depth입니다.

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:pattern3": "node pattern3.mjs"
+  },
+  "devDependencies": {
+    "playwright-core": "1.62.0"
+  }
+}

e2e/pattern3.mjs

@@ -0,0 +1,198 @@
+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:8083/") {
+      return;
+    }
+    if (attempt === 1) {
+      await page.goto(
+        "http://localhost:8083/oauth2/authorization/keycloak",
+      );
+      await page.waitForURL(/localhost:8080/u);
+    }
+  }
+  throw new Error(`Keycloak login did not return to AP3: ${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();
+  const browserRequests = [];
+  page.on("request", (request) =>
+    browserRequests.push({ method: request.method(), url: request.url() }),
+  );
+
+  await page.goto("http://localhost:8083");
+  const authorizationRequestPromise = page.waitForRequest((request) =>
+    request.url().includes(
+      "/protocol/openid-connect/auth?response_type=code",
+    ),
+  );
+  await page.locator("#login").click();
+  const authorizationRequest = await authorizationRequestPromise;
+  const authorizationUrl = new URL(authorizationRequest.url());
+  assert.equal(authorizationUrl.searchParams.get("client_id"), "bff-confidential");
+  assert.equal(authorizationUrl.searchParams.get("code_challenge_method"), "S256");
+  assert.ok(authorizationUrl.searchParams.get("code_challenge"));
+
+  await page.waitForURL(/localhost:8080/u);
+  await completeKeycloakLogin(page);
+  const callbackRequest = browserRequests.find(({ url }) =>
+    url.startsWith("http://localhost:8083/login/oauth2/code/keycloak?"),
+  );
+  assert.ok(callbackRequest, "authorization response must use the BFF callback");
+  assert.equal(callbackRequest.method, "GET");
+
+  const boundaryResponsePromise = page.waitForResponse((response) =>
+    response.url().endsWith("/bff/token-boundary"),
+  );
+  await page.locator("#inspect").click();
+  const boundaryResponse = await boundaryResponsePromise;
+  assert.equal(boundaryResponse.status(), 200);
+  const boundary = await boundaryResponse.json();
+  assert.equal(boundary.accessTokenStoredOnServer, true);
+  assert.equal(boundary.refreshTokenStoredOnServer, true);
+  assert.equal(boundary.browserTokenCount, 0);
+  assert.equal(boundary.csrfProtectionEnabled, true);
+  assert.equal(JSON.stringify(boundary).includes("access_token"), false);
+  assert.equal(JSON.stringify(boundary).includes("refresh_token"), false);
+
+  const proxyResponsePromise = page.waitForResponse((response) =>
+    response.url().endsWith("/bff/api/me"),
+  );
+  await page.locator("#call-bff").click();
+  const proxyResponse = await proxyResponsePromise;
+  assert.equal(proxyResponse.status(), 200);
+  const resource = await proxyResponse.json();
+  assert.equal(resource.username, "regular-user");
+  assert.ok(resource.audience.includes("keycloak-pattern-api"));
+
+  assert.equal(
+    browserRequests.some(({ url }) =>
+      url.startsWith("http://localhost:8081/"),
+    ),
+    false,
+    "the browser must not bypass the BFF",
+  );
+  assert.equal(
+    browserRequests.some(({ url }) =>
+      url.includes("/protocol/openid-connect/token"),
+    ),
+    false,
+    "the token exchange must be server-to-server",
+  );
+
+  const cookies = await context.cookies("http://localhost:8083/");
+  const sessionCookie = cookies.find((cookie) => cookie.name === "AP3_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),
+    readableCookies: document.cookie,
+  }));
+  assert.deepEqual(storage.localStorage, []);
+  assert.deepEqual(storage.sessionStorage, []);
+  assert.equal(storage.readableCookies.includes("AP3_SESSION"), false);
+
+  const missingCsrfResponse = await page.evaluate(async () => {
+    const response = await fetch("/bff/api/preferences", {
+      method: "POST",
+      body: new URLSearchParams({ theme: "missing-csrf" }),
+      headers: { "Content-Type": "application/x-www-form-urlencoded" },
+    });
+    return response.status;
+  });
+  assert.equal(missingCsrfResponse, 403);
+
+  const csrfResponsePromise = page.waitForResponse((response) =>
+    response.url().endsWith("/bff/csrf"),
+  );
+  const validChangeResponsePromise = page.waitForResponse(
+    (response) =>
+      response.url().endsWith("/bff/api/preferences") &&
+      response.request().method() === "POST" &&
+      response.status() === 200,
+  );
+  await page.locator("#change-with-csrf").click();
+  const csrfResponse = await csrfResponsePromise;
+  const validChangeResponse = await validChangeResponsePromise;
+  assert.equal(csrfResponse.status(), 200);
+  assert.equal(validChangeResponse.status(), 200);
+  const validChange = await validChangeResponse.json();
+  assert.equal(validChange.theme, "dark");
+
+  const csrfCookies = await context.cookies("http://localhost:8083/");
+  const csrfCookie = csrfCookies.find((cookie) => cookie.name === "XSRF-TOKEN");
+  assert.ok(csrfCookie);
+  assert.equal(csrfCookie.httpOnly, false);
+
+  await page.goto("http://localhost:8088");
+  const [forgedResponse] = await Promise.all([
+    page.waitForNavigation(),
+    page.evaluate(() => {
+      const form = document.createElement("form");
+      form.method = "POST";
+      form.action = "http://localhost:8083/bff/api/preferences";
+      const input = document.createElement("input");
+      input.name = "theme";
+      input.value = "attacker";
+      form.append(input);
+      document.body.append(form);
+      form.submit();
+    }),
+  ]);
+  assert.ok(forgedResponse);
+  assert.equal(forgedResponse.status(), 403);
+
+  await page.goto("http://127.0.0.1:8088");
+  const crossSiteRequestPromise = page.waitForRequest(
+    (request) =>
+      request.url() === "http://localhost:8083/bff/api/preferences" &&
+      request.method() === "POST",
+  );
+  await page.evaluate(() => {
+    const form = document.createElement("form");
+    form.method = "POST";
+    form.action = "http://localhost:8083/bff/api/preferences";
+    const input = document.createElement("input");
+    input.name = "theme";
+    input.value = "cross-site-attacker";
+    form.append(input);
+    document.body.append(form);
+    form.submit();
+  });
+  const crossSiteRequest = await crossSiteRequestPromise;
+  const crossSiteHeaders = await crossSiteRequest.allHeaders();
+  assert.equal(
+    (crossSiteHeaders.cookie ?? "").includes("AP3_SESSION="),
+    false,
+    "SameSite=Lax must omit the session cookie on a cross-site POST",
+  );
+
+  console.log(
+    "pattern3 BFF verified: tokenless POST 403, CSRF header 200, SameSite=Lax session",
+  );
+} finally {
+  await browser.close();
+}

keycloak/import/keycloak-patterns-realm.json

@@ -98,8 +98,24 @@
         "http://localhost:8083"
       ],
       "attributes": {
+        "pkce.code.challenge.method": "S256",
         "post.logout.redirect.uris": "http://localhost:8083/*"
-      }
+      },
+      "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": "edge-proxy",

scripts/verify-pattern3.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:pattern3
+
+echo "AP3 BFF session and CSRF behavior verified"