Cloud Identity-Aware Proxy (IAP) is a Google Cloud service that provides centralized authentication and authorization for applications. When combined with Java applications, it enables secure access control without modifying application code.
What is Cloud IAP?
Cloud IAP provides:
- Zero-trust security model - verify every request
- Centralized access control - manage permissions in one place
- Context-aware access - consider device, location, and user identity
- SSL termination - handle TLS/SSL at the proxy level
- Audit logging - comprehensive access logs
Dependencies and Setup
Maven Configuration:
<dependencies> <!-- Google Cloud IAP --> <dependency> <groupId>com.google.cloud</groupId> <artifactId>google-cloud-iap</artifactId> <version>2.4.0</version> </dependency> <!-- Google Auth Library --> <dependency> <groupId>com.google.auth</groupId> <artifactId>google-auth-library-oauth2-http</artifactId> <version>1.19.0</version> </dependency> <!-- Spring Security --> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-security</artifactId> </dependency> <!-- JWT Processing --> <dependency> <groupId>com.auth0</groupId> <artifactId>java-jwt</artifactId> <version>4.4.0</version> </dependency> <!-- HTTP Client --> <dependency> <groupId>org.apache.httpcomponents.client5</groupId> <artifactId>httpclient5</artifactId> <version>5.2.1</version> </dependency> </dependencies>
IAP Configuration Properties
IapProperties.java:
@Configuration
@ConfigurationProperties(prefix = "gcp.iap")
@Data
public class IapProperties {
// GCP Project configuration
private String projectId;
private String projectNumber;
// IAP-specific configuration
private String backendServiceId;
private String audience;
private String issuer = "https://cloud.google.com/iap";
// JWT validation
private String jwksUrl = "https://www.gstatic.com/iap/verify/public_key-jwk";
private long clockSkewSeconds = 300; // 5 minutes
// Security settings
private boolean enabled = true;
private boolean requireIapHeader = true;
private List<String> excludedPaths = Arrays.asList("/health", "/actuator/**");
// Header configuration
private String userEmailHeader = "X-Goog-Authenticated-User-Email";
private String userIdHeader = "X-Goog-Authenticated-User-ID";
private String iapJwtHeader = "X-Goog-IAP-JWT-Assertion";
public String getExpectedAudience() {
if (audience != null) {
return audience;
}
return String.format("/projects/%s/apps/%s",
projectNumber, projectId);
}
}
JWT Token Verification
IapTokenVerifier.java:
@Component
@Slf4j
public class IapTokenVerifier {
private final IapProperties iapProperties;
private final JwkProvider jwkProvider;
private final ObjectMapper objectMapper;
public IapTokenVerifier(IapProperties iapProperties) {
this.iapProperties = iapProperties;
this.jwkProvider = new GoogleJwkProvider(iapProperties.getJwksUrl());
this.objectMapper = new ObjectMapper();
}
public IapClaims verifyIapToken(String jwtToken) {
try {
JWT jwt = JWTParser.parse(jwtToken);
// Verify signature
Jwk jwk = jwkProvider.get(jwt.getHeader().getKeyId());
Algorithm algorithm = getAlgorithm(jwk);
JWTVerifier verifier = getVerifier(algorithm);
DecodedJWT decodedJWT = verifier.verify(jwtToken);
// Verify claims
verifyClaims(decodedJWT);
return extractClaims(decodedJWT);
} catch (Exception e) {
log.error("IAP token verification failed", e);
throw new IapVerificationException("Token verification failed", e);
}
}
private Algorithm getAlgorithm(Jwk jwk) {
if (jwk.getAlgorithm() == null) {
return Algorithm.RSA256((RSAPublicKey) jwk.getPublicKey(), null);
}
switch (jwk.getAlgorithm().getName()) {
case "RS256":
return Algorithm.RSA256((RSAPublicKey) jwk.getPublicKey(), null);
case "ES256":
return Algorithm.ECDSA256((ECPublicKey) jwk.getPublicKey(), null);
default:
throw new UnsupportedAlgorithmException("Unsupported algorithm: " + jwk.getAlgorithm());
}
}
private JWTVerifier getVerifier(Algorithm algorithm) {
return JWT.require(algorithm)
.acceptLeeway(iapProperties.getClockSkewSeconds())
.build();
}
private void verifyClaims(DecodedJWT decodedJWT) {
String audience = decodedJWT.getAudience().get(0);
String expectedAudience = iapProperties.getExpectedAudience();
if (!expectedAudience.equals(audience)) {
throw new InvalidAudienceException(
String.format("Invalid audience: %s, expected: %s",
audience, expectedAudience));
}
if (!iapProperties.getIssuer().equals(decodedJWT.getIssuer())) {
throw new InvalidIssuerException(
String.format("Invalid issuer: %s", decodedJWT.getIssuer()));
}
// Verify token is not expired
if (decodedJWT.getExpiresAt().before(new Date())) {
throw new TokenExpiredException("Token has expired");
}
}
private IapClaims extractClaims(DecodedJWT decodedJWT) {
try {
String payload = new String(
Base64.getUrlDecoder().decode(decodedJWT.getPayload())
);
IapClaims claims = objectMapper.readValue(payload, IapClaims.class);
claims.setRawToken(decodedJWT.getToken());
return claims;
} catch (Exception e) {
throw new ClaimsExtractionException("Failed to extract claims", e);
}
}
@Data
public static class IapClaims {
private String iss;
private String aud;
private Long exp;
private Long iat;
private String sub;
private String email;
private String hd;
private String rawToken;
public Instant getExpiration() {
return Instant.ofEpochSecond(exp);
}
public Instant getIssuedAt() {
return Instant.ofEpochSecond(iat);
}
public boolean isExpired() {
return getExpiration().isBefore(Instant.now());
}
}
}
Spring Security Configuration
IapSecurityConfig.java:
@Configuration
@EnableWebSecurity
@EnableGlobalMethodSecurity(prePostEnabled = true)
@Slf4j
public class IapSecurityConfig {
private final IapProperties iapProperties;
private final IapTokenVerifier tokenVerifier;
private final IapUserService iapUserService;
public IapSecurityConfig(IapProperties iapProperties,
IapTokenVerifier tokenVerifier,
IapUserService iapUserService) {
this.iapProperties = iapProperties;
this.tokenVerifier = tokenVerifier;
this.iapUserService = iapUserService;
}
@Bean
public SecurityFilterChain securityFilterChain(HttpSecurity http) throws Exception {
http
.csrf(csrf -> csrf.disable())
.sessionManagement(session -> session.sessionCreationPolicy(SessionCreationPolicy.STATELESS))
.authorizeHttpRequests(authz -> authz
.requestMatchers(iapProperties.getExcludedPaths().toArray(new String[0])).permitAll()
.anyRequest().authenticated()
)
.addFilterBefore(iapAuthenticationFilter(), UsernamePasswordAuthenticationFilter.class)
.exceptionHandling(exceptions -> exceptions
.authenticationEntryPoint(iapAuthenticationEntryPoint())
);
return http.build();
}
@Bean
public IapAuthenticationFilter iapAuthenticationFilter() {
return new IapAuthenticationFilter(tokenVerifier, iapUserService, iapProperties);
}
@Bean
public IapAuthenticationEntryPoint iapAuthenticationEntryPoint() {
return new IapAuthenticationEntryPoint();
}
@Bean
public AuthenticationManager authenticationManager() {
return new ProviderManager(Arrays.asList(iapAuthenticationProvider()));
}
@Bean
public IapAuthenticationProvider iapAuthenticationProvider() {
return new IapAuthenticationProvider(iapUserService);
}
}
IAP Authentication Filter
IapAuthenticationFilter.java:
@Slf4j
public class IapAuthenticationFilter extends OncePerRequestFilter {
private final IapTokenVerifier tokenVerifier;
private final IapUserService iapUserService;
private final IapProperties iapProperties;
public IapAuthenticationFilter(IapTokenVerifier tokenVerifier,
IapUserService iapUserService,
IapProperties iapProperties) {
this.tokenVerifier = tokenVerifier;
this.iapUserService = iapUserService;
this.iapProperties = iapProperties;
}
@Override
protected void doFilterInternal(HttpServletRequest request,
HttpServletResponse response,
FilterChain filterChain) throws ServletException, IOException {
if (shouldNotFilter(request)) {
filterChain.doFilter(request, response);
return;
}
try {
String jwtToken = extractJwtToken(request);
if (jwtToken == null) {
if (iapProperties.isRequireIapHeader()) {
throw new IapAuthenticationException("Missing IAP JWT token");
} else {
filterChain.doFilter(request, response);
return;
}
}
// Verify the JWT token
IapTokenVerifier.IapClaims claims = tokenVerifier.verifyIapToken(jwtToken);
// Create authentication object
IapAuthenticationToken authentication = createAuthentication(claims, request);
// Set authentication in security context
SecurityContextHolder.getContext().setAuthentication(authentication);
filterChain.doFilter(request, response);
} catch (IapAuthenticationException e) {
SecurityContextHolder.clearContext();
response.sendError(HttpStatus.UNAUTHORIZED.value(), e.getMessage());
} catch (Exception e) {
log.error("IAP authentication failed", e);
SecurityContextHolder.clearContext();
response.sendError(HttpStatus.INTERNAL_SERVER_ERROR.value(), "Authentication failed");
}
}
@Override
protected boolean shouldNotFilter(HttpServletRequest request) {
String path = request.getRequestURI();
// Skip excluded paths
return iapProperties.getExcludedPaths().stream()
.anyMatch(excluded -> path.matches(excluded.replace("**", ".*")));
}
private String extractJwtToken(HttpServletRequest request) {
// Try to get token from IAP header
String token = request.getHeader(iapProperties.getIapJwtHeader());
if (token != null) {
return token;
}
// Fallback to Authorization header
String authHeader = request.getHeader("Authorization");
if (authHeader != null && authHeader.startsWith("Bearer ")) {
return authHeader.substring(7);
}
return null;
}
private IapAuthenticationToken createAuthentication(IapTokenVerifier.IapClaims claims,
HttpServletRequest request) {
String userEmail = extractUserEmail(request, claims);
IapUser user = iapUserService.loadUserByEmail(userEmail);
return new IapAuthenticationToken(user, claims, user.getAuthorities());
}
private String extractUserEmail(HttpServletRequest request, IapTokenVerifier.IapClaims claims) {
// Try to get email from IAP header first
String headerEmail = request.getHeader(iapProperties.getUserEmailHeader());
if (headerEmail != null) {
return headerEmail.replace("accounts.google.com:", "");
}
// Fallback to claims
if (claims.getEmail() != null) {
return claims.getEmail();
}
throw new IapAuthenticationException("Unable to extract user email from request");
}
}
IAP Authentication Components
IapAuthenticationToken.java:
public class IapAuthenticationToken extends AbstractAuthenticationToken {
private final IapUser principal;
private final IapTokenVerifier.IapClaims credentials;
public IapAuthenticationToken(IapUser principal,
IapTokenVerifier.IapClaims credentials,
Collection<? extends GrantedAuthority> authorities) {
super(authorities);
this.principal = principal;
this.credentials = credentials;
super.setAuthenticated(true);
}
@Override
public Object getCredentials() {
return credentials;
}
@Override
public Object getPrincipal() {
return principal;
}
@Override
public String getName() {
return principal.getEmail();
}
}
IapAuthenticationProvider.java:
@Component
public class IapAuthenticationProvider implements AuthenticationProvider {
private final IapUserService iapUserService;
public IapAuthenticationProvider(IapUserService iapUserService) {
this.iapUserService = iapUserService;
}
@Override
public Authentication authenticate(Authentication authentication) throws AuthenticationException {
if (!supports(authentication.getClass())) {
return null;
}
IapAuthenticationToken iapToken = (IapAuthenticationToken) authentication;
IapUser user = (IapUser) iapToken.getPrincipal();
// Additional validation can be performed here
if (!user.isEnabled()) {
throw new DisabledException("User account is disabled");
}
return iapToken;
}
@Override
public boolean supports(Class<?> authentication) {
return IapAuthenticationToken.class.isAssignableFrom(authentication);
}
}
IapAuthenticationEntryPoint.java:
@Component
public class IapAuthenticationEntryPoint implements AuthenticationEntryPoint {
@Override
public void commence(HttpServletRequest request,
HttpServletResponse response,
AuthenticationException authException) throws IOException {
response.setContentType("application/json");
response.setStatus(HttpStatus.UNAUTHORIZED.value());
ErrorResponse error = new ErrorResponse(
"UNAUTHORIZED",
"IAP authentication required",
request.getRequestURI(),
Instant.now()
);
ObjectMapper mapper = new ObjectMapper();
response.getWriter().write(mapper.writeValueAsString(error));
}
@Data
@AllArgsConstructor
public static class ErrorResponse {
private String error;
private String message;
private String path;
private Instant timestamp;
}
}
User Management Service
IapUserService.java:
@Service
@Slf4j
public class IapUserService {
private final UserRepository userRepository;
private final RoleService roleService;
public IapUserService(UserRepository userRepository, RoleService roleService) {
this.userRepository = userRepository;
this.roleService = roleService;
}
public IapUser loadUserByEmail(String email) {
UserEntity userEntity = userRepository.findByEmail(email)
.orElseGet(() -> createNewUser(email));
return convertToIapUser(userEntity);
}
public IapUser loadUserById(String userId) {
UserEntity userEntity = userRepository.findById(userId)
.orElseThrow(() -> new UserNotFoundException("User not found: " + userId));
return convertToIapUser(userEntity);
}
private UserEntity createNewUser(String email) {
log.info("Creating new user for email: {}", email);
UserEntity newUser = new UserEntity();
newUser.setEmail(email);
newUser.setEnabled(true);
newUser.setCreatedAt(Instant.now());
newUser.setLastLogin(Instant.now());
// Assign default role
Role defaultRole = roleService.getDefaultRole();
newUser.setRoles(Set.of(defaultRole));
return userRepository.save(newUser);
}
private IapUser convertToIapUser(UserEntity userEntity) {
Set<GrantedAuthority> authorities = userEntity.getRoles().stream()
.flatMap(role -> role.getPermissions().stream())
.map(permission -> new SimpleGrantedAuthority(permission.name()))
.collect(Collectors.toSet());
// Add role-based authorities
userEntity.getRoles().forEach(role ->
authorities.add(new SimpleGrantedAuthority("ROLE_" + role.getName())));
return IapUser.builder()
.id(userEntity.getId())
.email(userEntity.getEmail())
.enabled(userEntity.isEnabled())
.authorities(authorities)
.createdAt(userEntity.getCreatedAt())
.lastLogin(userEntity.getLastLogin())
.build();
}
public void updateLastLogin(String email) {
userRepository.findByEmail(email).ifPresent(user -> {
user.setLastLogin(Instant.now());
userRepository.save(user);
});
}
}
IapUser.java:
@Data
@Builder
public class IapUser implements UserDetails {
private String id;
private String email;
private boolean enabled;
private Collection<? extends GrantedAuthority> authorities;
private Instant createdAt;
private Instant lastLogin;
@Override
public String getUsername() {
return email;
}
@Override
public String getPassword() {
return null; // No password in IAP authentication
}
@Override
public boolean isAccountNonExpired() {
return true;
}
@Override
public boolean isAccountNonLocked() {
return true;
}
@Override
public boolean isCredentialsNonExpired() {
return true;
}
}
Role and Permission Management
RoleService.java:
@Service
@Slf4j
public class RoleService {
private final RoleRepository roleRepository;
public RoleService(RoleRepository roleRepository) {
this.roleRepository = roleRepository;
initializeDefaultRoles();
}
public Role getDefaultRole() {
return roleRepository.findByName("USER")
.orElseThrow(() -> new RuntimeException("Default role not found"));
}
public Role getRoleByName(String name) {
return roleRepository.findByName(name)
.orElseThrow(() -> new RoleNotFoundException("Role not found: " + name));
}
public Set<Permission> getPermissionsForRole(String roleName) {
return getRoleByName(roleName).getPermissions();
}
public boolean hasPermission(String roleName, Permission permission) {
return getPermissionsForRole(roleName).contains(permission);
}
private void initializeDefaultRoles() {
if (roleRepository.count() == 0) {
log.info("Initializing default roles");
Role userRole = new Role();
userRole.setName("USER");
userRole.setDescription("Basic user role");
userRole.setPermissions(Set.of(Permission.READ, Permission.WRITE_SELF));
Role adminRole = new Role();
adminRole.setName("ADMIN");
adminRole.setDescription("Administrator role");
adminRole.setPermissions(Set.of(Permission.values()));
Role viewerRole = new Role();
viewerRole.setName("VIEWER");
viewerRole.setDescription("Read-only user role");
viewerRole.setPermissions(Set.of(Permission.READ));
roleRepository.saveAll(Arrays.asList(userRole, adminRole, viewerRole));
}
}
public enum Permission {
READ, WRITE, WRITE_SELF, DELETE, ADMINISTER
}
}
IAP Health Check and Monitoring
IapHealthIndicator.java:
@Component
@Slf4j
public class IapHealthIndicator implements HealthIndicator {
private final IapProperties iapProperties;
private final IapTokenVerifier tokenVerifier;
public IapHealthIndicator(IapProperties iapProperties, IapTokenVerifier tokenVerifier) {
this.iapProperties = iapProperties;
this.tokenVerifier = tokenVerifier;
}
@Override
public Health health() {
try {
if (!iapProperties.isEnabled()) {
return Health.up()
.withDetail("enabled", false)
.withDetail("message", "IAP is disabled")
.build();
}
// Test JWT verification by checking if we can fetch JWKS
testJwksAvailability();
return Health.up()
.withDetail("enabled", true)
.withDetail("projectId", iapProperties.getProjectId())
.withDetail("audience", iapProperties.getExpectedAudience())
.withDetail("issuer", iapProperties.getIssuer())
.build();
} catch (Exception e) {
log.error("IAP health check failed", e);
return Health.down(e)
.withDetail("enabled", true)
.withDetail("error", e.getMessage())
.build();
}
}
private void testJwksAvailability() {
try {
// This would typically involve fetching the JWKS endpoint
// to verify connectivity and response format
HttpGet request = new HttpGet(iapProperties.getJwksUrl());
try (CloseableHttpClient client = HttpClients.createDefault();
CloseableHttpResponse response = client.execute(request)) {
if (response.getCode() != 200) {
throw new IOException("JWKS endpoint returned: " + response.getCode());
}
}
} catch (Exception e) {
throw new IapHealthException("JWKS endpoint unavailable", e);
}
}
}
Request Context and User Information
IapRequestContext.java:
@Component
@Slf4j
public class IapRequestContext {
public Optional<IapUser> getCurrentUser() {
Authentication authentication = SecurityContextHolder.getContext().getAuthentication();
if (authentication != null &&
authentication.isAuthenticated() &&
authentication.getPrincipal() instanceof IapUser) {
return Optional.of((IapUser) authentication.getPrincipal());
}
return Optional.empty();
}
public String getCurrentUserId() {
return getCurrentUser()
.map(IapUser::getId)
.orElseThrow(() -> new NoUserContextException("No user in security context"));
}
public String getCurrentUserEmail() {
return getCurrentUser()
.map(IapUser::getEmail)
.orElseThrow(() -> new NoUserContextException("No user in security context"));
}
public boolean hasPermission(Permission permission) {
return getCurrentUser()
.map(user -> user.getAuthorities().stream()
.anyMatch(auth -> auth.getAuthority().equals(permission.name())))
.orElse(false);
}
public boolean hasRole(String role) {
String roleAuthority = "ROLE_" + role.toUpperCase();
return getCurrentUser()
.map(user -> user.getAuthorities().stream()
.anyMatch(auth -> auth.getAuthority().equals(roleAuthority)))
.orElse(false);
}
}
REST Controller with IAP Protection
SecureApiController.java:
@RestController
@RequestMapping("/api/secure")
@Slf4j
public class SecureApiController {
private final IapRequestContext iapContext;
private final UserRepository userRepository;
public SecureApiController(IapRequestContext iapContext, UserRepository userRepository) {
this.iapContext = iapContext;
this.userRepository = userRepository;
}
@GetMapping("/user/profile")
@PreAuthorize("isAuthenticated()")
public ResponseEntity<UserProfile> getUserProfile() {
String userEmail = iapContext.getCurrentUserEmail();
UserEntity user = userRepository.findByEmail(userEmail)
.orElseThrow(() -> new UserNotFoundException("User not found: " + userEmail));
UserProfile profile = UserProfile.builder()
.id(user.getId())
.email(user.getEmail())
.roles(user.getRoles().stream().map(Role::getName).collect(Collectors.toSet()))
.createdAt(user.getCreatedAt())
.lastLogin(user.getLastLogin())
.build();
return ResponseEntity.ok(profile);
}
@GetMapping("/admin/users")
@PreAuthorize("hasRole('ADMIN')")
public ResponseEntity<List<UserProfile>> getAllUsers() {
List<UserProfile> users = userRepository.findAll().stream()
.map(this::convertToProfile)
.collect(Collectors.toList());
return ResponseEntity.ok(users);
}
@PostMapping("/user/preferences")
@PreAuthorize("hasPermission('WRITE_SELF')")
public ResponseEntity<Void> updateUserPreferences(@RequestBody UserPreferences preferences) {
String userId = iapContext.getCurrentUserId();
// Update user preferences logic
log.info("Updating preferences for user: {}", userId);
return ResponseEntity.ok().build();
}
private UserProfile convertToProfile(UserEntity user) {
return UserProfile.builder()
.id(user.getId())
.email(user.getEmail())
.roles(user.getRoles().stream().map(Role::getName).collect(Collectors.toSet()))
.createdAt(user.getCreatedAt())
.lastLogin(user.getLastLogin())
.build();
}
@Data
@Builder
public static class UserProfile {
private String id;
private String email;
private Set<String> roles;
private Instant createdAt;
private Instant lastLogin;
}
@Data
public static class UserPreferences {
private String theme;
private String language;
private boolean notificationsEnabled;
}
}
Application Configuration
application.yml:
gcp:
iap:
enabled: true
project-id: ${GCP_PROJECT_ID:my-project}
project-number: ${GCP_PROJECT_NUMBER:123456789}
backend-service-id: ${IAP_BACKEND_SERVICE_ID:}
audience: ${IAP_AUDIENCE:}
require-iap-header: true
clock-skew-seconds: 300
excluded-paths:
- "/health"
- "/actuator/**"
- "/public/**"
spring:
security:
oauth2:
resourceserver:
jwt:
issuer-uri: https://cloud.google.com/iap
logging:
level:
com.example.iap: DEBUG
Best Practices for IAP Implementation
- Always validate JWT tokens - never trust headers without verification
- Implement proper error handling for authentication failures
- Use role-based access control for fine-grained permissions
- Monitor IAP health and token verification failures
- Implement graceful degradation when IAP is unavailable
- Regularly rotate IAP credentials and monitor for security updates
- Use context-aware access policies for additional security layers
Conclusion
Cloud IAP with Java provides a robust, zero-trust security layer for your applications:
- Centralized authentication without application changes
- Fine-grained authorization with Spring Security integration
- Comprehensive audit logging and monitoring
- Seamless Google Workspace integration for user management
- Production-ready security with automatic token verification
By implementing Cloud IAP with the Java stack shown above, organizations can secure their applications with enterprise-grade identity and access management while maintaining developer productivity and operational efficiency.
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