Article
In the evolution of OAuth 2.0 and OpenID Connect, traditional authentication flows require user interaction through a browser redirect. However, modern use cases—smart TVs, IoT devices, CLI tools, and authentication via mobile apps—demand a decoupled approach where the device requesting authentication cannot directly display a login page. CIBA (Client-Initiated Backchannel Authentication) addresses this need by allowing clients to initiate authentication and receive authorization through a separate, out-of-band channel.
What is CIBA?
CIBA is an extension to OpenID Connect that enables a client application to initiate an authentication request without redirecting the user's browser. Instead, the authentication happens on a separate device (like a mobile phone), and the client receives the result via a backchannel.
Key characteristics of CIBA:
- Decoupled Flow: Authentication happens on a different device than the requesting client
- Out-of-Band Verification: User approves on their trusted device
- Backchannel Communication: Client and authorization server communicate directly
- Asynchronous Operation: Authentication may take seconds or minutes to complete
- Polling or Ping: Client can poll for results or receive a notification
CIBA Flow Overview
┌─────────┐ ┌──────────────┐ ┌─────────┐ │ Client │ │ Auth Server │ │ User │ │(Device) │ │ │ │(Phone) │ └────┬────┘ └──────┬───────┘ └────┬────┘ │ │ │ │ 1. Authentication │ │ │ Request │ │ ├─────────────────────>│ │ │ │ │ │ 2. auth_req_id │ │ │<─────────────────────┤ │ │ │ │ │ │ 3. Push Notification │ │ │ or out-of-band │ │ ├──────────────────────>│ │ │ │ │ │ 4. User Authenticates│ │ │ and Consents │ │ │<──────────────────────┤ │ │ │ │ 5. Poll for token │ │ │ (with auth_req_id) │ │ ├─────────────────────>│ │ │ │ │ │ 6. Return tokens │ │ │<─────────────────────┤ │ ┌────┴────┐ ┌──────┴───────┐ ┌────┴────┐ │ Client │ │ Auth Server │ │ User │ │(Device) │ │ │ │(Phone) │ └─────────┘ └──────────────┘ └─────────┘
Why CIBA for Java Applications?
- Headless Devices: Smart TVs, IoT devices, CLI tools without browsers
- Improved UX: Users authenticate on trusted devices (phones)
- Step-Up Authentication: Add extra verification for sensitive operations
- Transaction Approval: Approve specific transactions out-of-band
- Passwordless Authentication: Use device biometrics for authentication
Implementing CIBA in Java
1. CIBA Request Model
import lombok.Data;
import lombok.Builder;
import javax.validation.constraints.NotBlank;
import javax.validation.constraints.NotNull;
import java.util.List;
import java.util.Map;
@Data
@Builder
public class CibaAuthenticationRequest {
@NotBlank
private String clientId;
@NotBlank
private String clientSecret;
@NotBlank
private String scope;
@NotBlank
private String bindingMessage;
private String loginHint;
private String userCode;
private String requestedExpiry;
private List<String> acrValues;
private Map<String, Object> claims;
private String transactionContext;
@Builder.Default
private int requestTimeoutSeconds = 120;
@Builder.Default
private CibaRequestType requestType = CibaRequestType.LOGIN;
public enum CibaRequestType {
LOGIN,
TRANSACTION_AUTH,
STEP_UP,
CONSENT
}
}
@Data
@Builder
public class CibaResponse {
@NotBlank
private String authReqId;
private int expiresIn;
private int interval;
@Builder.Default
private CibaStatus status = CibaStatus.PENDING;
public enum CibaStatus {
PENDING,
AUTHORIZED,
REJECTED,
EXPIRED
}
}
2. CIBA Authentication Service
import org.springframework.stereotype.Service;
import java.security.SecureRandom;
import java.time.Instant;
import java.util.Base64;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
@Service
public class CibaAuthenticationService {
private final Map<String, CibaSession> activeSessions = new ConcurrentHashMap<>();
private final SecureRandom secureRandom = new SecureRandom();
private final DeviceNotificationService notificationService;
private final TokenService tokenService;
public CibaResponse initiateAuthentication(CibaAuthenticationRequest request) {
// Validate client
validateClient(request.getClientId(), request.getClientSecret());
// Generate unique auth request ID
String authReqId = generateAuthReqId();
// Create session
CibaSession session = CibaSession.builder()
.authReqId(authReqId)
.clientId(request.getClientId())
.scope(request.getScope())
.bindingMessage(request.getBindingMessage())
.loginHint(request.getLoginHint())
.status(CibaStatus.PENDING)
.createdAt(Instant.now())
.expiresAt(Instant.now().plusSeconds(request.getRequestTimeoutSeconds()))
.requestType(request.getRequestType())
.transactionContext(request.getTransactionContext())
.build();
activeSessions.put(authReqId, session);
// Send push notification to user's device
notificationService.sendAuthenticationRequest(session);
return CibaResponse.builder()
.authReqId(authReqId)
.expiresIn(request.getRequestTimeoutSeconds())
.interval(2) // Polling interval in seconds
.status(CibaStatus.PENDING)
.build();
}
public CibaResponse checkAuthenticationStatus(String authReqId) {
CibaSession session = activeSessions.get(authReqId);
if (session == null) {
throw new CibaException("Invalid auth_req_id");
}
if (session.getExpiresAt().isBefore(Instant.now())) {
activeSessions.remove(authReqId);
return CibaResponse.builder()
.authReqId(authReqId)
.status(CibaStatus.EXPIRED)
.build();
}
return CibaResponse.builder()
.authReqId(authReqId)
.status(session.getStatus())
.build();
}
public TokenResponse completeAuthentication(String authReqId, String userId) {
CibaSession session = activeSessions.get(authReqId);
if (session == null || session.getStatus() != CibaStatus.PENDING) {
throw new CibaException("Invalid or expired session");
}
// Update session status
session.setStatus(CibaStatus.AUTHORIZED);
session.setUserId(userId);
session.setAuthorizedAt(Instant.now());
// Generate tokens
TokenResponse tokens = tokenService.generateTokens(
userId,
session.getClientId(),
session.getScope()
);
// Store tokens for later retrieval via token endpoint
session.setTokens(tokens);
return tokens;
}
public void rejectAuthentication(String authReqId, String reason) {
CibaSession session = activeSessions.get(authReqId);
if (session != null) {
session.setStatus(CibaStatus.REJECTED);
session.setRejectionReason(reason);
}
}
public TokenResponse pollForToken(String authReqId, String clientId, String clientSecret) {
CibaSession session = activeSessions.get(authReqId);
if (session == null) {
throw new CibaException("Invalid auth_req_id");
}
if (!session.getClientId().equals(clientId)) {
throw new CibaException("Client mismatch");
}
switch (session.getStatus()) {
case AUTHORIZED:
activeSessions.remove(authReqId);
return session.getTokens();
case REJECTED:
activeSessions.remove(authReqId);
throw new CibaRejectedException(session.getRejectionReason());
case EXPIRED:
activeSessions.remove(authReqId);
throw new CibaExpiredException();
default:
throw new CibaPendingException();
}
}
private String generateAuthReqId() {
byte[] randomBytes = new byte[32];
secureRandom.nextBytes(randomBytes);
return Base64.getUrlEncoder().withoutPadding().encodeToString(randomBytes);
}
@Data
@Builder
private static class CibaSession {
private String authReqId;
private String clientId;
private String scope;
private String bindingMessage;
private String loginHint;
private CibaStatus status;
private Instant createdAt;
private Instant expiresAt;
private Instant authorizedAt;
private String userId;
private CibaRequestType requestType;
private String transactionContext;
private TokenResponse tokens;
private String rejectionReason;
}
}
3. CIBA REST Controllers
import org.springframework.web.bind.annotation.*;
import org.springframework.http.ResponseEntity;
@RestController
@RequestMapping("/oauth/ciba")
public class CibaController {
@Autowired
private CibaAuthenticationService cibaService;
@Autowired
private ClientAuthenticationService clientAuthService;
/**
* CIBA Authentication Request Endpoint
* Client initiates authentication request
*/
@PostMapping("/auth-request")
public ResponseEntity<CibaResponse> initiateAuth(
@RequestBody CibaAuthenticationRequest request) {
CibaResponse response = cibaService.initiateAuthentication(request);
return ResponseEntity.ok(response);
}
/**
* CIBA Authentication Status Endpoint
* Client checks status (alternative to polling)
*/
@GetMapping("/status/{authReqId}")
public ResponseEntity<CibaResponse> checkStatus(
@PathVariable String authReqId,
@RequestHeader("Authorization") String clientAuth) {
// Validate client authentication
clientAuthService.validateClient(clientAuth);
CibaResponse response = cibaService.checkAuthenticationStatus(authReqId);
return ResponseEntity.ok(response);
}
/**
* CIBA Token Endpoint
* Client exchanges auth_req_id for tokens after approval
*/
@PostMapping("/token")
public ResponseEntity<TokenResponse> getToken(
@RequestParam("auth_req_id") String authReqId,
@RequestHeader("Authorization") String clientAuth) {
// Extract client credentials
ClientCredentials credentials = clientAuthService.extractCredentials(clientAuth);
TokenResponse tokens = cibaService.pollForToken(
authReqId,
credentials.getClientId(),
credentials.getClientSecret()
);
return ResponseEntity.ok(tokens);
}
}
4. User Device Endpoints (Mobile App Backend)
@RestController
@RequestMapping("/api/ciba/user")
public class CibaUserController {
@Autowired
private CibaAuthenticationService cibaService;
@Autowired
private UserAuthenticationService userAuthService;
/**
* Get pending authentication requests for user
*/
@GetMapping("/pending")
public ResponseEntity<List<PendingAuthRequest>> getPendingRequests(
@RequestHeader("Authorization") String userToken) {
String userId = userAuthService.validateToken(userToken);
List<PendingAuthRequest> pendingRequests = cibaService.getPendingRequestsForUser(userId);
return ResponseEntity.ok(pendingRequests);
}
/**
* Approve authentication request from mobile device
*/
@PostMapping("/approve/{authReqId}")
public ResponseEntity<ApprovalResponse> approveRequest(
@PathVariable String authReqId,
@RequestBody ApprovalRequest approval,
@RequestHeader("Authorization") String userToken) {
String userId = userAuthService.validateToken(userToken);
// Verify binding message matches
verifyBindingMessage(authReqId, approval.getBindingMessage());
// Verify transaction context if present
verifyTransactionContext(authReqId, approval.getTransactionContext());
TokenResponse tokens = cibaService.completeAuthentication(authReqId, userId);
return ResponseEntity.ok(ApprovalResponse.builder()
.status("APPROVED")
.message("Authentication approved")
.build());
}
/**
* Reject authentication request from mobile device
*/
@PostMapping("/reject/{authReqId}")
public ResponseEntity<ApprovalResponse> rejectRequest(
@PathVariable String authReqId,
@RequestBody RejectionRequest rejection,
@RequestHeader("Authorization") String userToken) {
String userId = userAuthService.validateToken(userToken);
cibaService.rejectAuthentication(authReqId, rejection.getReason());
return ResponseEntity.ok(ApprovalResponse.builder()
.status("REJECTED")
.message("Authentication rejected")
.build());
}
@Data
@Builder
public static class PendingAuthRequest {
private String authReqId;
private String clientName;
private String bindingMessage;
private String scope;
private Instant requestedAt;
private String transactionContext;
private CibaRequestType requestType;
}
}
5. Push Notification Service
@Service
public class DeviceNotificationService {
@Autowired
private FirebaseMessaging firebaseMessaging;
@Autowired
private UserDeviceRegistry deviceRegistry;
public void sendAuthenticationRequest(CibaSession session) {
// Find user's devices based on login_hint
List<UserDevice> devices = deviceRegistry.findDevicesByUserHint(
session.getLoginHint());
for (UserDevice device : devices) {
Notification notification = Notification.builder()
.setTitle("Authentication Request")
.setBody(session.getBindingMessage())
.build();
Map<String, String> data = new HashMap<>();
data.put("authReqId", session.getAuthReqId());
data.put("clientId", session.getClientId());
data.put("type", "CIBA_AUTH_REQUEST");
data.put("bindingMessage", session.getBindingMessage());
data.put("timestamp", String.valueOf(Instant.now().toEpochMilli()));
if (session.getTransactionContext() != null) {
data.put("transactionContext", session.getTransactionContext());
}
Message message = Message.builder()
.setToken(device.getFcmToken())
.setNotification(notification)
.putAllData(data)
.setApnsConfig(ApnsConfig.builder()
.putHeader("apns-priority", "10")
.build())
.setAndroidConfig(AndroidConfig.builder()
.setPriority(AndroidConfig.Priority.HIGH)
.build())
.build();
try {
String response = firebaseMessaging.send(message);
log.info("Sent push notification to device: {}", response);
} catch (FirebaseMessagingException e) {
log.error("Failed to send push notification", e);
}
}
}
}
6. CIBA Token Endpoint Implementation
@RestController
@RequestMapping("/oauth/token")
public class CibaTokenEndpoint {
@Autowired
private CibaAuthenticationService cibaService;
@Autowired
private TokenService tokenService;
/**
* OAuth 2.0 Token Endpoint with CIBA grant type support
*/
@PostMapping
public ResponseEntity<TokenResponse> token(
@RequestParam("grant_type") String grantType,
@RequestParam(value = "auth_req_id", required = false) String authReqId,
@RequestParam(value = "code", required = false) String code,
@RequestParam(value = "refresh_token", required = false) String refreshToken,
@RequestParam(value = "redirect_uri", required = false) String redirectUri,
@RequestHeader("Authorization") String clientAuth) {
ClientCredentials credentials = extractClientCredentials(clientAuth);
if ("urn:openid:params:grant-type:ciba".equals(grantType)) {
// CIBA grant type - polling for token
return handleCibaGrant(authReqId, credentials);
} else if ("authorization_code".equals(grantType)) {
// Standard OAuth2 grant
return handleAuthCodeGrant(code, redirectUri, credentials);
} else if ("refresh_token".equals(grantType)) {
// Refresh token grant
return handleRefreshToken(refreshToken, credentials);
} else {
return ResponseEntity.badRequest().build();
}
}
private ResponseEntity<TokenResponse> handleCibaGrant(
String authReqId,
ClientCredentials credentials) {
try {
TokenResponse tokens = cibaService.pollForToken(
authReqId,
credentials.getClientId(),
credentials.getClientSecret()
);
return ResponseEntity.ok(tokens);
} catch (CibaPendingException e) {
return ResponseEntity.status(HttpStatus.BAD_REQUEST)
.header("Cache-Control", "no-store")
.body(TokenResponse.error("authorization_pending"));
} catch (CibaExpiredException e) {
return ResponseEntity.status(HttpStatus.BAD_REQUEST)
.body(TokenResponse.error("expired_token"));
} catch (CibaRejectedException e) {
return ResponseEntity.status(HttpStatus.BAD_REQUEST)
.body(TokenResponse.error("access_denied"));
}
}
}
7. CIBA Request Validation
@Component
public class CibaRequestValidator {
@Autowired
private ClientRepository clientRepository;
@Autowired
private UserRepository userRepository;
public ValidationResult validateRequest(CibaAuthenticationRequest request) {
List<String> violations = new ArrayList<>();
// Validate client
if (!validateClient(request.getClientId(), request.getClientSecret())) {
violations.add("Invalid client credentials");
}
// Validate scope
if (!validateScope(request.getScope())) {
violations.add("Invalid scope");
}
// Validate binding message
if (request.getBindingMessage() == null ||
request.getBindingMessage().length() < 5) {
violations.add("Binding message must be at least 5 characters");
}
// Validate login hint (if provided)
if (request.getLoginHint() != null &&
!userRepository.existsByLoginHint(request.getLoginHint())) {
violations.add("Unknown user");
}
// Validate transaction context for transaction auth
if (request.getRequestType() == CibaRequestType.TRANSACTION_AUTH &&
request.getTransactionContext() == null) {
violations.add("Transaction context required for transaction auth");
}
return ValidationResult.builder()
.valid(violations.isEmpty())
.violations(violations)
.build();
}
}
8. Mobile App Integration (Android/iOS Backend)
@RestController
@RequestMapping("/api/mobile/auth")
public class MobileAuthController {
@Autowired
private CibaAuthenticationService cibaService;
@Autowired
private UserSessionService sessionService;
/**
* Device registration for push notifications
*/
@PostMapping("/register-device")
public ResponseEntity<DeviceRegistrationResponse> registerDevice(
@RequestBody DeviceRegistrationRequest request,
@RequestHeader("Authorization") String userToken) {
String userId = sessionService.validateToken(userToken);
UserDevice device = UserDevice.builder()
.userId(userId)
.fcmToken(request.getFcmToken())
.deviceId(request.getDeviceId())
.deviceName(request.getDeviceName())
.platform(request.getPlatform())
.registeredAt(Instant.now())
.build();
deviceRegistry.registerDevice(device);
return ResponseEntity.ok(DeviceRegistrationResponse.builder()
.status("registered")
.build());
}
/**
* Mobile-initiated CIBA request (e.g., scanning QR code)
*/
@PostMapping("/initiate-mobile")
public ResponseEntity<MobileCibaResponse> initiateMobileAuth(
@RequestBody MobileCibaRequest request) {
// Validate QR code or deep link data
CibaAuthenticationRequest cibaRequest = CibaAuthenticationRequest.builder()
.clientId(request.getClientId())
.scope(request.getScope())
.bindingMessage(request.getBindingMessage())
.loginHint(request.getLoginHint()) // May be extracted from QR code
.requestTimeoutSeconds(120)
.build();
CibaResponse response = cibaService.initiateAuthentication(cibaRequest);
return ResponseEntity.ok(MobileCibaResponse.builder()
.authReqId(response.getAuthReqId())
.bindingMessage(request.getBindingMessage())
.expiresIn(response.getExpiresIn())
.build());
}
}
9. CIBA with Step-Up Authentication
@Service
public class StepUpCibaService {
@Autowired
private CibaAuthenticationService cibaService;
@Autowired
private TokenService tokenService;
/**
* Initiate step-up authentication for sensitive operation
*/
public StepUpResult initiateStepUp(String currentToken, String operation) {
// Validate current token
TokenValidationResult validation = tokenService.validateToken(currentToken);
if (validation.isValid() &&
validation.getAcrLevel() >= AcrLevel.LEVEL_2) {
// Already sufficiently authenticated
return StepUpResult.alreadyAuthenticated();
}
// Create CIBA request for step-up
CibaAuthenticationRequest request = CibaAuthenticationRequest.builder()
.clientId(validation.getClientId())
.scope("openid step_up")
.bindingMessage("Approve sensitive operation: " + operation)
.loginHint(validation.getUserId())
.requestType(CibaRequestType.STEP_UP)
.acrValues(List.of("phr", "phrh"))
.transactionContext(operation)
.build();
CibaResponse response = cibaService.initiateAuthentication(request);
return StepUpResult.builder()
.stepUpRequired(true)
.authReqId(response.getAuthReqId())
.expiresIn(response.getExpiresIn())
.build();
}
/**
* Complete step-up and issue upgraded token
*/
public TokenResponse completeStepUp(String authReqId, String userId) {
TokenResponse upgradedTokens = cibaService.completeAuthentication(authReqId, userId);
// Enhance token with higher ACR level
return tokenService.upgradeTokenWithAcr(upgradedTokens, AcrLevel.LEVEL_3);
}
}
10. CIBA Configuration Properties
@ConfigurationProperties(prefix = "ciba")
@Data
public class CibaProperties {
private boolean enabled = true;
private RequestDefaults request = new RequestDefaults();
private Polling polling = new Polling();
private PushNotification push = new PushNotification();
private Security security = new Security();
@Data
public static class RequestDefaults {
private int defaultTimeoutSeconds = 120;
private int maxTimeoutSeconds = 600;
private String defaultBindingMessage = "Please approve this login request";
}
@Data
public static class Polling {
private int minInterval = 2;
private int maxInterval = 30;
private int maxPollingDuration = 600;
}
@Data
public static class PushNotification {
private boolean enabled = true;
private String fcmConfigPath = "firebase-config.json";
private int notificationTtlSeconds = 300;
}
@Data
public static class Security {
private boolean requireSignedRequests = false;
private boolean validateBindingMessage = true;
private int maxActiveRequestsPerUser = 5;
private String signatureAlgorithm = "RS256";
}
}
11. application.yml Configuration
ciba: enabled: true request: default-timeout-seconds: 120 max-timeout-seconds: 300 default-binding-message: "Please approve this request on your phone" polling: min-interval: 2 max-interval: 5 max-polling-duration: 600 push: enabled: true fcm-config-path: classpath:firebase-adminsdk.json notification-ttl-seconds: 300 security: max-active-requests-per-user: 5 validate-binding-message: true spring: security: oauth2: resourceserver: jwt: issuer-uri: https://auth-server.example.com server: port: 8080
Testing CIBA Implementation
@SpringBootTest
@AutoConfigureMockMvc
class CibaIntegrationTest {
@Autowired
private MockMvc mockMvc;
@Autowired
private CibaAuthenticationService cibaService;
@Test
void testCibaFullFlow() throws Exception {
// 1. Initiate CIBA request
CibaAuthenticationRequest request = CibaAuthenticationRequest.builder()
.clientId("test-client")
.clientSecret("test-secret")
.scope("openid profile")
.bindingMessage("Test login request")
.loginHint("[email protected]")
.build();
String requestJson = new ObjectMapper().writeValueAsString(request);
MvcResult initiateResult = mockMvc.perform(post("/oauth/ciba/auth-request")
.contentType(MediaType.APPLICATION_JSON)
.content(requestJson))
.andExpect(status().isOk())
.andReturn();
CibaResponse cibaResponse = new ObjectMapper().readValue(
initiateResult.getResponse().getContentAsString(),
CibaResponse.class);
assertNotNull(cibaResponse.getAuthReqId());
// 2. Simulate user approval on mobile device
cibaService.completeAuthentication(cibaResponse.getAuthReqId(), "test-user");
// 3. Poll for token
MvcResult tokenResult = mockMvc.perform(post("/oauth/token")
.param("grant_type", "urn:openid:params:grant-type:ciba")
.param("auth_req_id", cibaResponse.getAuthReqId())
.header("Authorization", "Basic " +
Base64.getEncoder().encodeToString("test-client:test-secret".getBytes())))
.andExpect(status().isOk())
.andReturn();
TokenResponse tokenResponse = new ObjectMapper().readValue(
tokenResult.getResponse().getContentAsString(),
TokenResponse.class);
assertNotNull(tokenResponse.getAccessToken());
}
}
Security Considerations
- Binding Message: Always display a clear binding message to prevent phishing
- Request Signing: Consider signed requests using JWT for non-repudiation
- Rate Limiting: Limit CIBA requests per user to prevent denial-of-service
- Push Notification Security: Use secure push notification services (FCM, APNS)
- Transaction Context: Include transaction details for approval
- Expiration: Always set reasonable expiration times
- Client Authentication: Strongly authenticate clients making CIBA requests
Best Practices
- Clear User Communication: Display binding messages that match across channels
- Appropriate Timeouts: Set timeouts based on use case (login vs transaction)
- Polling Intervals: Use exponential backoff for polling
- Device Registration: Maintain secure device registry with push tokens
- Fallback Mechanisms: Provide alternative authentication methods
- Audit Logging: Log all CIBA requests and approvals
- Multi-Factor: Combine with device biometrics for step-up auth
Conclusion
CIBA provides a powerful, standards-based approach to decoupled authentication that addresses the limitations of traditional redirect-based flows. For Java applications, implementing CIBA enables:
- Headless device authentication for IoT, smart TVs, and CLI tools
- Enhanced security through out-of-band verification
- Improved user experience with mobile-based approval
- Step-up authentication for sensitive operations
- Transaction signing with clear user context
As authentication continues to evolve beyond the browser, CIBA offers a robust foundation for scenarios where the requesting device cannot or should not handle user credentials directly. By integrating CIBA into your Java authentication server, you provide modern, flexible authentication options while maintaining the security and standards compliance of OAuth 2.0 and OpenID Connect.
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Read more: https://macronepal.com/blog/arrays-in-java/
While Loop in Java:
A while loop repeats a block of code as long as a given condition remains true. It is useful when the number of repetitions is not known beforehand.
Read more: https://macronepal.com/blog/while-loop-in-java/