Building Production-Ready Authentication Systems: A Complete Guide

Authentication is the gatekeeper of your application. Get it wrong, and you're either frustrating legitimate users or leaving your system vulnerable to attacks. In this comprehensive guide, I'll walk you through building a production-ready authentication system that balances security, usability, and maintainability.

Authentication vs Authorization: Getting the Basics Right

Before diving into implementation, let's clarify the fundamentals:

Authentication: Verifying who a user is ("I am John")
Authorization: Determining what a user can do ("John can edit posts")

Many developers conflate these concepts, leading to security vulnerabilities. Keep them separate in your design.

Choosing Your Authentication Strategy

Option 1: Session-Based Authentication

Traditional cookie-based sessions work well for:

Server-rendered applications
Single domain deployments
Applications requiring strict session control

@RestController
@RequestMapping("/api/auth")
public class SessionAuthController {
    
    @PostMapping("/login")
    public ResponseEntity<?> login(@RequestBody LoginRequest request, 
                                   HttpSession session) {
        // Validate credentials
        User user = authService.authenticate(
            request.getUsername(), 
            request.getPassword()
        );
        
        // Create session
        session.setAttribute("userId", user.getId());
        session.setAttribute("roles", user.getRoles());
        
        return ResponseEntity.ok(new AuthResponse(user));
    }
    
    @PostMapping("/logout")
    public ResponseEntity<?> logout(HttpSession session) {
        session.invalidate();
        return ResponseEntity.ok().build();
    }
}

Option 2: Token-Based Authentication (JWT)

JWTs are ideal for:

Stateless microservices
Mobile applications
Cross-domain scenarios
Distributed systems

@Component
public class JwtTokenProvider {
    
    @Value("${jwt.secret}")
    private String jwtSecret;
    
    @Value("${jwt.expiration}")
    private int jwtExpiration;
    
    public String generateToken(Authentication authentication) {
        UserPrincipal userPrincipal = (UserPrincipal) authentication.getPrincipal();
        
        Date expiryDate = new Date(System.currentTimeMillis() + jwtExpiration);
        
        return Jwts.builder()
                .setSubject(Long.toString(userPrincipal.getId()))
                .setIssuedAt(new Date())
                .setExpiration(expiryDate)
                .claim("roles", userPrincipal.getAuthorities())
                .signWith(SignatureAlgorithm.HS512, jwtSecret)
                .compact();
    }
    
    public boolean validateToken(String authToken) {
        try {
            Jwts.parser().setSigningKey(jwtSecret).parseClaimsJws(authToken);
            return true;
        } catch (SignatureException ex) {
            log.error("Invalid JWT signature");
        } catch (MalformedJwtException ex) {
            log.error("Invalid JWT token");
        } catch (ExpiredJwtException ex) {
            log.error("Expired JWT token");
        } catch (UnsupportedJwtException ex) {
            log.error("Unsupported JWT token");
        } catch (IllegalArgumentException ex) {
            log.error("JWT claims string is empty");
        }
        return false;
    }
}

Implementing JWT-Based Authentication

Step 1: User Registration

@Service
@Transactional
public class AuthService {
    
    private final UserRepository userRepository;
    private final PasswordEncoder passwordEncoder;
    private final JwtTokenProvider tokenProvider;
    
    public AuthResponse registerUser(SignUpRequest signUpRequest) {
        // Check if username exists
        if (userRepository.existsByUsername(signUpRequest.getUsername())) {
            throw new BadRequestException("Username already taken!");
        }
        
        // Check if email exists
        if (userRepository.existsByEmail(signUpRequest.getEmail())) {
            throw new BadRequestException("Email already in use!");
        }
        
        // Create new user
        User user = new User();
        user.setUsername(signUpRequest.getUsername());
        user.setEmail(signUpRequest.getEmail());
        user.setPassword(passwordEncoder.encode(signUpRequest.getPassword()));
        user.setRoles(Collections.singleton(Role.ROLE_USER));
        
        User savedUser = userRepository.save(user);
        
        // Generate token
        String token = tokenProvider.generateToken(
            new UsernamePasswordAuthenticationToken(
                savedUser.getId(), 
                null, 
                savedUser.getAuthorities()
            )
        );
        
        return new AuthResponse(token, savedUser);
    }
}

Step 2: Secure Password Storage

Never store passwords in plain text. Use a strong hashing algorithm:

@Configuration
@EnableWebSecurity
public class SecurityConfig extends WebSecurityConfigurerAdapter {
    
    @Bean
    public PasswordEncoder passwordEncoder() {
        return new BCryptPasswordEncoder(12); // 12 rounds
    }
    
    @Bean
    public AuthenticationManager authenticationManagerBean() throws Exception {
        return super.authenticationManagerBean();
    }
}

Step 3: JWT Authentication Filter

@Component
public class JwtAuthenticationFilter extends OncePerRequestFilter {
    
    @Autowired
    private JwtTokenProvider tokenProvider;
    
    @Autowired
    private CustomUserDetailsService customUserDetailsService;
    
    @Override
    protected void doFilterInternal(HttpServletRequest request, 
                                    HttpServletResponse response, 
                                    FilterChain filterChain) 
                                    throws ServletException, IOException {
        try {
            String jwt = getJwtFromRequest(request);
            
            if (StringUtils.hasText(jwt) && tokenProvider.validateToken(jwt)) {
                Long userId = tokenProvider.getUserIdFromJWT(jwt);
                
                UserDetails userDetails = customUserDetailsService.loadUserById(userId);
                UsernamePasswordAuthenticationToken authentication = 
                    new UsernamePasswordAuthenticationToken(
                        userDetails, 
                        null, 
                        userDetails.getAuthorities()
                    );
                authentication.setDetails(
                    new WebAuthenticationDetailsSource().buildDetails(request)
                );
                
                SecurityContextHolder.getContext().setAuthentication(authentication);
            }
        } catch (Exception ex) {
            logger.error("Could not set user authentication in security context", ex);
        }
        
        filterChain.doFilter(request, response);
    }
    
    private String getJwtFromRequest(HttpServletRequest request) {
        String bearerToken = request.getHeader("Authorization");
        if (StringUtils.hasText(bearerToken) && bearerToken.startsWith("Bearer ")) {
            return bearerToken.substring(7);
        }
        return null;
    }
}

Session Management Best Practices

1. Implement Refresh Tokens

Don't make your access tokens long-lived. Use refresh tokens:

@Entity
@Table(name = "refresh_tokens")
public class RefreshToken {
    @Id
    @GeneratedValue(strategy = GenerationType.UUID)
    private String id;
    
    @OneToOne
    @JoinColumn(name = "user_id", referencedColumnName = "id")
    private User user;
    
    @Column(nullable = false, unique = true)
    private String token;
    
    @Column(nullable = false)
    private Instant expiryDate;
    
    // getters and setters
}

@Service
public class RefreshTokenService {
    
    @Value("${jwt.refresh.expiration}")
    private Long refreshTokenDurationMs;
    
    @Autowired
    private RefreshTokenRepository refreshTokenRepository;
    
    public RefreshToken createRefreshToken(Long userId) {
        RefreshToken refreshToken = new RefreshToken();
        
        refreshToken.setUser(userRepository.findById(userId).get());
        refreshToken.setExpiryDate(Instant.now().plusMillis(refreshTokenDurationMs));
        refreshToken.setToken(UUID.randomUUID().toString());
        
        refreshToken = refreshTokenRepository.save(refreshToken);
        return refreshToken;
    }
    
    public RefreshToken verifyExpiration(RefreshToken token) {
        if (token.getExpiryDate().compareTo(Instant.now()) < 0) {
            refreshTokenRepository.delete(token);
            throw new TokenRefreshException(token.getToken(), 
                "Refresh token was expired. Please make a new signin request");
        }
        
        return token;
    }
}

2. Implement Logout Properly

For JWT-based systems, maintain a token blacklist:

@Service
public class TokenBlacklistService {
    
    private final RedisTemplate<String, String> redisTemplate;
    
    public void blacklistToken(String token, long expirationTime) {
        redisTemplate.opsForValue().set(
            "blacklist_" + token, 
            "true", 
            expirationTime, 
            TimeUnit.MILLISECONDS
        );
    }
    
    public boolean isBlacklisted(String token) {
        return redisTemplate.hasKey("blacklist_" + token);
    }
}

OAuth 2.0 and Social Login

Implementing Google OAuth

@Configuration
@EnableWebSecurity
@EnableGlobalMethodSecurity(prePostEnabled = true)
public class SecurityConfig extends WebSecurityConfigurerAdapter {
    
    @Autowired
    private CustomOAuth2UserService customOAuth2UserService;
    
    @Override
    protected void configure(HttpSecurity http) throws Exception {
        http
            .cors()
                .and()
            .csrf()
                .disable()
            .sessionManagement()
                .sessionCreationPolicy(SessionCreationPolicy.STATELESS)
                .and()
            .authorizeRequests()
                .antMatchers("/auth/**", "/oauth2/**")
                    .permitAll()
                .anyRequest()
                    .authenticated()
                .and()
            .oauth2Login()
                .authorizationEndpoint()
                    .baseUri("/oauth2/authorize")
                    .authorizationRequestRepository(cookieAuthorizationRequestRepository())
                    .and()
                .redirectionEndpoint()
                    .baseUri("/oauth2/callback/*")
                    .and()
                .userInfoEndpoint()
                    .userService(customOAuth2UserService)
                    .and()
                .successHandler(oAuth2AuthenticationSuccessHandler)
                .failureHandler(oAuth2AuthenticationFailureHandler);
        
        http.addFilterBefore(tokenAuthenticationFilter(), UsernamePasswordAuthenticationFilter.class);
    }
}

Custom OAuth2 User Service

@Service
public class CustomOAuth2UserService extends DefaultOAuth2UserService {
    
    @Autowired
    private UserRepository userRepository;
    
    @Override
    public OAuth2User loadUser(OAuth2UserRequest oAuth2UserRequest) throws OAuth2AuthenticationException {
        OAuth2User oAuth2User = super.loadUser(oAuth2UserRequest);
        
        try {
            return processOAuth2User(oAuth2UserRequest, oAuth2User);
        } catch (AuthenticationException ex) {
            throw ex;
        } catch (Exception ex) {
            throw new InternalAuthenticationServiceException(ex.getMessage(), ex.getCause());
        }
    }
    
    private OAuth2User processOAuth2User(OAuth2UserRequest oAuth2UserRequest, OAuth2User oAuth2User) {
        OAuth2UserInfo oAuth2UserInfo = OAuth2UserInfoFactory.getOAuth2UserInfo(
            oAuth2UserRequest.getClientRegistration().getRegistrationId(), 
            oAuth2User.getAttributes()
        );
        
        if(StringUtils.isEmpty(oAuth2UserInfo.getEmail())) {
            throw new OAuth2AuthenticationProcessingException("Email not found from OAuth2 provider");
        }
        
        Optional<User> userOptional = userRepository.findByEmail(oAuth2UserInfo.getEmail());
        User user;
        
        if(userOptional.isPresent()) {
            user = userOptional.get();
            if(!user.getProvider().equals(AuthProvider.valueOf(
                oAuth2UserRequest.getClientRegistration().getRegistrationId()))) {
                throw new OAuth2AuthenticationProcessingException("You're signed up with " +
                    user.getProvider() + " account. Please use your " + user.getProvider() +
                    " account to login.");
            }
            user = updateExistingUser(user, oAuth2UserInfo);
        } else {
            user = registerNewUser(oAuth2UserRequest, oAuth2UserInfo);
        }
        
        return UserPrincipal.create(user, oAuth2User.getAttributes());
    }
}

Security Considerations

1. Rate Limiting

Prevent brute force attacks:

@Component
public class RateLimitingFilter extends OncePerRequestFilter {
    
    private final RateLimiter rateLimiter = RateLimiter.create(10.0); // 10 requests per second
    
    @Override
    protected void doFilterInternal(HttpServletRequest request, 
                                    HttpServletResponse response, 
                                    FilterChain filterChain) 
                                    throws ServletException, IOException {
        if (request.getRequestURI().startsWith("/auth/")) {
            if (!rateLimiter.tryAcquire()) {
                response.setStatus(HttpStatus.TOO_MANY_REQUESTS.value());
                response.getWriter().write("Too many requests");
                return;
            }
        }
        
        filterChain.doFilter(request, response);
    }
}

2. Account Lockout

Implement progressive delays after failed attempts:

@Service
public class LoginAttemptService {
    
    private final int MAX_ATTEMPT = 5;
    private LoadingCache<String, Integer> attemptsCache;
    
    public LoginAttemptService() {
        super();
        attemptsCache = CacheBuilder.newBuilder()
            .expireAfterWrite(1, TimeUnit.DAYS)
            .build(new CacheLoader<String, Integer>() {
                @Override
                public Integer load(String key) {
                    return 0;
                }
            });
    }
    
    public void loginFailed(String key) {
        int attempts = 0;
        try {
            attempts = attemptsCache.get(key);
        } catch (ExecutionException e) {
            attempts = 0;
        }
        attempts++;
        attemptsCache.put(key, attempts);
    }
    
    public boolean isBlocked(String key) {
        try {
            return attemptsCache.get(key) >= MAX_ATTEMPT;
        } catch (ExecutionException e) {
            return false;
        }
    }
}

3. CSRF Protection

For session-based auth, always use CSRF tokens:

@Configuration
public class SecurityConfig extends WebSecurityConfigurerAdapter {
    
    @Override
    protected void configure(HttpSecurity http) throws Exception {
        http
            .csrf()
                .csrfTokenRepository(CookieCsrfTokenRepository.withHttpOnlyFalse())
                .and()
            // ... other configuration
    }
}

Authentication at Scale

When your system grows from thousands to millions of users, authentication becomes one of the most critical performance bottlenecks. Here's how to scale authentication effectively.

Distributed Session Management Architecture

The Challenge: At scale, session management can consume 40-60% of your Redis cluster capacity if not properly architected.

@Configuration
public class DistributedSessionConfig {
    
    // Partition sessions across multiple Redis nodes
    @Bean
    public RedisTemplate<String, Object> sessionRedisTemplate(
            @Value("${redis.session.nodes}") String[] nodes) {
        
        RedisClusterConfiguration clusterConfig = new RedisClusterConfiguration(
            Arrays.asList(nodes)
        );
        
        // Enable read from replicas for better performance
        LettuceClientConfiguration clientConfig = LettuceClientConfiguration.builder()
            .readFrom(ReadFrom.REPLICA_PREFERRED)
            .commandTimeout(Duration.ofMillis(500))
            .build();
            
        LettuceConnectionFactory factory = new LettuceConnectionFactory(
            clusterConfig, clientConfig
        );
        
        RedisTemplate<String, Object> template = new RedisTemplate<>();
        template.setConnectionFactory(factory);
        
        // Use Kryo for 3x better serialization performance
        template.setDefaultSerializer(new KryoRedisSerializer());
        
        return template;
    }
    
    @Bean
    public SessionRegistry distributedSessionRegistry() {
        return new RedisBackedSessionRegistry(sessionRedisTemplate()) {
            @Override
            protected String computeSessionKey(String sessionId) {
                // Distribute sessions across shards based on user ID
                int shard = sessionId.hashCode() % 16;
                return String.format("session:shard:%d:%s", shard, sessionId);
            }
        };
    }
}

Performance Benchmarks:

# Session Storage Performance Comparison (1M concurrent sessions)
storage_type:
  in_memory:
    read_latency_p99: 0.1ms
    write_latency_p99: 0.2ms
    max_capacity: 10k sessions
    failover: none
    
  redis_standalone:
    read_latency_p99: 1ms
    write_latency_p99: 2ms
    max_capacity: 100k sessions
    failover: sentinel
    
  redis_cluster:
    read_latency_p99: 2ms
    write_latency_p99: 3ms
    max_capacity: 10M sessions
    failover: automatic
    
  dynamodb:
    read_latency_p99: 10ms
    write_latency_p99: 15ms
    max_capacity: unlimited
    failover: multi-region

Zero-Trust Architecture Implementation

In modern distributed systems, zero-trust is not optional—it's essential.

@Component
public class ZeroTrustAuthenticationManager {
    
    private final DeviceTrustEvaluator deviceTrust;
    private final NetworkContextEvaluator networkContext;
    private final BehaviorAnalyzer behaviorAnalyzer;
    private final RiskScoreCalculator riskCalculator;
    
    public AuthenticationDecision authenticate(AuthenticationRequest request) {
        // Never trust, always verify
        RiskProfile risk = RiskProfile.builder()
            .deviceTrust(deviceTrust.evaluate(request.getDeviceFingerprint()))
            .networkRisk(networkContext.evaluate(request.getClientIP()))
            .behaviorScore(behaviorAnalyzer.analyze(request.getUserId()))
            .build();
            
        double riskScore = riskCalculator.calculate(risk);
        
        if (riskScore > 0.8) {
            // High risk - deny or require step-up authentication
            return AuthenticationDecision.stepUpRequired(
                StepUpMethod.HARDWARE_TOKEN
            );
        } else if (riskScore > 0.5) {
            // Medium risk - require MFA
            return AuthenticationDecision.mfaRequired();
        }
        
        // Low risk - proceed with continuous verification
        return AuthenticationDecision.allow()
            .withContinuousVerification(Duration.ofMinutes(15));
    }
    
    @EventListener
    public void onSecurityEvent(SecurityEvent event) {
        // Real-time risk adjustment
        if (event.getType() == SecurityEventType.ANOMALY_DETECTED) {
            // Immediately revoke all sessions for affected user
            sessionRegistry.revokeAllSessions(event.getUserId());
            
            // Notify security team
            securityAlertService.alert(event);
        }
    }
}

Multi-Factor Authentication Patterns at Scale

Adaptive MFA Based on Risk Scoring:

@Service
public class AdaptiveMFAService {
    
    private final Map<MFAMethod, MFAProvider> providers = new ConcurrentHashMap<>();
    
    @PostConstruct
    public void initProviders() {
        // Register providers in order of security strength
        providers.put(MFAMethod.SMS, new SMSProvider()); // Weakest
        providers.put(MFAMethod.TOTP, new TOTPProvider());
        providers.put(MFAMethod.PUSH, new PushNotificationProvider());
        providers.put(MFAMethod.WEBAUTHN, new WebAuthnProvider());
        providers.put(MFAMethod.HARDWARE_TOKEN, new HardwareTokenProvider()); // Strongest
    }
    
    public MFAChallenge createChallenge(User user, RiskScore risk) {
        // Select MFA method based on risk
        List<MFAMethod> requiredMethods = new ArrayList<>();
        
        if (risk.getValue() > 0.9) {
            // Ultra high risk - require multiple factors
            requiredMethods.add(MFAMethod.HARDWARE_TOKEN);
            requiredMethods.add(MFAMethod.PUSH);
        } else if (risk.getValue() > 0.7) {
            // High risk - strong factor required
            requiredMethods.add(user.hasWebAuthn() ? 
                MFAMethod.WEBAUTHN : MFAMethod.TOTP);
        } else if (risk.getValue() > 0.3) {
            // Medium risk - any registered factor
            requiredMethods.add(user.getPreferredMFAMethod());
        }
        // Low risk - no MFA required
        
        return MFAChallenge.builder()
            .userId(user.getId())
            .requiredMethods(requiredMethods)
            .expiresIn(Duration.ofMinutes(5))
            .build();
    }
}

// WebAuthn implementation for strongest security
@Component
public class WebAuthnProvider implements MFAProvider {
    
    private final RelyingParty relyingParty;
    
    @Override
    public AuthenticationChallenge createChallenge(User user) {
        // Generate challenge for hardware security key
        PublicKeyCredentialRequestOptions options = 
            PublicKeyCredentialRequestOptions.builder()
                .challenge(generateChallenge())
                .rpId(relyingParty.getId())
                .userVerification(UserVerificationRequirement.REQUIRED)
                .timeout(60000L)
                .allowCredentials(user.getWebAuthnCredentials())
                .build();
                
        return new WebAuthnChallenge(options);
    }
}

Federated Identity Management

Enterprise-Grade SAML/OIDC Integration:

@Configuration
@EnableFederatedIdentity
public class FederatedIdentityConfig {
    
    @Bean
    public IdentityProviderRegistry identityProviderRegistry() {
        return new DynamicIdentityProviderRegistry() {
            @Override
            protected void configure() {
                // Support multiple identity providers per tenant
                registerProvider("okta", OktaSAMLProvider.class);
                registerProvider("auth0", Auth0OIDCProvider.class);
                registerProvider("azure-ad", AzureADProvider.class);
                registerProvider("ping", PingFederateProvider.class);
            }
        };
    }
    
    @Bean
    public FederatedAuthenticationManager federatedAuthManager() {
        return new FederatedAuthenticationManager() {
            
            @Override
            public Authentication authenticate(FederatedAuthRequest request) {
                // Tenant-specific IdP resolution
                Tenant tenant = tenantResolver.resolve(request);
                IdentityProvider idp = identityProviderRegistry
                    .getProvider(tenant.getIdentityProvider());
                    
                // Validate SAML assertion or OIDC token
                FederatedIdentity identity = idp.validateAssertion(
                    request.getAssertion()
                );
                
                // Map external identity to internal user
                User user = userMappingService.mapOrCreate(
                    identity,
                    tenant,
                    MappingStrategy.JIT_PROVISIONING
                );
                
                // Apply tenant-specific policies
                applyTenantPolicies(user, tenant);
                
                return new FederatedAuthentication(user, identity);
            }
        };
    }
}

// Just-In-Time user provisioning
@Service
public class JITUserProvisioningService {
    
    @Transactional
    public User provisionUser(FederatedIdentity identity, Tenant tenant) {
        // Create user with federated identity
        User user = User.builder()
            .email(identity.getEmail())
            .username(generateUsername(identity, tenant))
            .federatedId(identity.getSubject())
            .identityProvider(identity.getProvider())
            .tenant(tenant)
            .build();
            
        // Apply tenant-specific attributes
        Map<String, Object> attributes = identity.getAttributes();
        if (tenant.getAttributeMapping() != null) {
            mapTenantAttributes(user, attributes, tenant.getAttributeMapping());
        }
        
        // Assign default roles based on IdP groups
        Set<Role> roles = roleMapper.mapFromGroups(
            identity.getGroups(),
            tenant.getRoleMapping()
        );
        user.setRoles(roles);
        
        return userRepository.save(user);
    }
}

Performance Benchmarks for Authentication Strategies

@Component
public class AuthenticationBenchmarkService {
    
    public BenchmarkResults runBenchmarks() {
        return BenchmarkResults.builder()
            .scenario("10k concurrent authentications")
            .results(Map.of(
                "jwt_validation", new BenchmarkResult(
                    "JWT Token Validation",
                    0.5, // ms p50
                    1.2, // ms p99
                    15000 // ops/sec/core
                ),
                "session_lookup", new BenchmarkResult(
                    "Redis Session Lookup",
                    1.0, // ms p50
                    3.5, // ms p99
                    8000 // ops/sec/core
                ),
                "oauth_token_exchange", new BenchmarkResult(
                    "OAuth Token Exchange",
                    50, // ms p50
                    150, // ms p99
                    200 // ops/sec/core
                ),
                "saml_assertion_validation", new BenchmarkResult(
                    "SAML Assertion Validation",
                    5, // ms p50
                    15, // ms p99
                    2000 // ops/sec/core
                ),
                "webauthn_verification", new BenchmarkResult(
                    "WebAuthn Verification",
                    10, // ms p50
                    25, // ms p99
                    1000 // ops/sec/core
                )
            ))
            .recommendations(List.of(
                "Use JWT for stateless services (highest throughput)",
                "Cache SAML metadata (10x performance improvement)",
                "Implement session affinity for 30% latency reduction",
                "Use connection pooling for Redis (2x throughput)"
            ))
            .build();
    }
}

Compliance Mapping

@Component
public class ComplianceMapper {
    
    public ComplianceReport mapAuthenticationToCompliance(
            AuthenticationConfig config) {
        
        Map<ComplianceStandard, ComplianceStatus> mapping = new HashMap<>();
        
        // SOC 2 Type II
        mapping.put(ComplianceStandard.SOC2_TYPE_II, 
            evaluateSOC2(config));
            
        // HIPAA
        mapping.put(ComplianceStandard.HIPAA, 
            evaluateHIPAA(config));
            
        // PCI DSS
        mapping.put(ComplianceStandard.PCI_DSS, 
            evaluatePCIDSS(config));
            
        // GDPR
        mapping.put(ComplianceStandard.GDPR, 
            evaluateGDPR(config));
            
        return new ComplianceReport(mapping);
    }
    
    private ComplianceStatus evaluateSOC2(AuthenticationConfig config) {
        List<ComplianceRequirement> requirements = List.of(
            new ComplianceRequirement(
                "CC6.1",
                "Logical and Physical Access Controls",
                config.hasMFA() && config.hasRBAC()
            ),
            new ComplianceRequirement(
                "CC6.7",
                "User Authentication via Unique Login",
                config.hasUniqueUserIdentification()
            ),
            new ComplianceRequirement(
                "CC6.8",
                "Failed Login Attempt Monitoring",
                config.hasLoginAttemptMonitoring()
            )
        );
        
        return ComplianceStatus.evaluate(requirements);
    }
    
    private ComplianceStatus evaluateHIPAA(AuthenticationConfig config) {
        List<ComplianceRequirement> requirements = List.of(
            new ComplianceRequirement(
                "164.312(a)(1)",
                "Access Control - Unique User Identification",
                config.hasUniqueUserIdentification()
            ),
            new ComplianceRequirement(
                "164.312(a)(2)",
                "Automatic Logoff",
                config.getSessionTimeout() <= Duration.ofMinutes(30)
            ),
            new ComplianceRequirement(
                "164.312(d)",
                "Person or Entity Authentication",
                config.hasMFA() || config.hasBiometric()
            )
        );
        
        return ComplianceStatus.evaluate(requirements);
    }
}

Scaling Authentication

@Configuration
@EnableRedisHttpSession
public class SessionConfig {
    
    @Bean
    public LettuceConnectionFactory connectionFactory() {
        return new LettuceConnectionFactory(
            new RedisStandaloneConfiguration("localhost", 6379)
        );
    }
    
    @Bean
    public HttpSessionIdResolver httpSessionIdResolver() {
        return HeaderHttpSessionIdResolver.xAuthToken();
    }
}

2. JWT Key Rotation

Implement key rotation for enhanced security:

@Component
public class JwtKeyRotationService {
    
    private final Map<String, Key> keyStore = new ConcurrentHashMap<>();
    private volatile String currentKeyId;
    
    @PostConstruct
    public void init() {
        rotateKey();
    }
    
    @Scheduled(cron = "0 0 0 * * ?") // Daily at midnight
    public void rotateKey() {
        String newKeyId = UUID.randomUUID().toString();
        Key newKey = Keys.secretKeyFor(SignatureAlgorithm.HS512);
        
        keyStore.put(newKeyId, newKey);
        currentKeyId = newKeyId;
        
        // Keep last 3 keys for validation of existing tokens
        if (keyStore.size() > 3) {
            String oldestKeyId = keyStore.keySet().iterator().next();
            keyStore.remove(oldestKeyId);
        }
    }
    
    public String getCurrentKeyId() {
        return currentKeyId;
    }
    
    public Key getKey(String keyId) {
        return keyStore.get(keyId);
    }
}

Testing Your Auth System

Integration Tests

@SpringBootTest
@AutoConfigureMockMvc
@TestPropertySource(locations = "classpath:application-test.properties")
public class AuthControllerIntegrationTest {
    
    @Autowired
    private MockMvc mockMvc;
    
    @Autowired
    private UserRepository userRepository;
    
    @Test
    public void testSuccessfulLogin() throws Exception {
        // Create test user
        User user = new User("testuser", "test@example.com", 
            passwordEncoder.encode("password123"));
        userRepository.save(user);
        
        LoginRequest loginRequest = new LoginRequest("testuser", "password123");
        
        mockMvc.perform(post("/auth/login")
                .contentType(MediaType.APPLICATION_JSON)
                .content(objectMapper.writeValueAsString(loginRequest)))
                .andExpect(status().isOk())
                .andExpect(jsonPath("$.accessToken").exists())
                .andExpect(jsonPath("$.tokenType").value("Bearer"));
    }
    
    @Test
    public void testLoginWithInvalidCredentials() throws Exception {
        LoginRequest loginRequest = new LoginRequest("invalid", "wrong");
        
        mockMvc.perform(post("/auth/login")
                .contentType(MediaType.APPLICATION_JSON)
                .content(objectMapper.writeValueAsString(loginRequest)))
                .andExpect(status().isUnauthorized());
    }
}

Security Tests

@Test
public void testRateLimiting() throws Exception {
    LoginRequest loginRequest = new LoginRequest("user", "pass");
    
    // Make 11 requests (limit is 10)
    for (int i = 0; i < 11; i++) {
        ResultActions result = mockMvc.perform(post("/auth/login")
                .contentType(MediaType.APPLICATION_JSON)
                .content(objectMapper.writeValueAsString(loginRequest)));
        
        if (i < 10) {
            result.andExpect(status().is4xxError());
        } else {
            result.andExpect(status().isTooManyRequests());
        }
    }
}

Common Pitfalls and How to Avoid Them

1. Storing Sensitive Data in JWTs

Don't do this:

// BAD: Sensitive data in JWT
claims.put("creditCard", user.getCreditCardNumber());
claims.put("ssn", user.getSocialSecurityNumber());

Do this instead:

// GOOD: Only non-sensitive identifiers
claims.put("userId", user.getId());
claims.put("roles", user.getRoles());

2. Not Validating Token Signature

Always validate:

public boolean validateToken(String authToken) {
    try {
        Jwts.parser()
            .setSigningKey(jwtSecret)
            .parseClaimsJws(authToken);
        return true;
    } catch (SignatureException ex) {
        log.error("Invalid JWT signature");
        return false;
    }
    // ... handle other exceptions
}

3. Using Weak Passwords

Implement password policies:

@Component
public class PasswordValidator {
    
    private static final String PASSWORD_PATTERN = 
        "^(?=.*[0-9])(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%^&+=])(?=\\S+$).{8,}$";
    
    private final Pattern pattern = Pattern.compile(PASSWORD_PATTERN);
    
    public boolean validate(String password) {
        return pattern.matcher(password).matches();
    }
}

Production Checklist

Before going to production, ensure:

[ ] Security Headers are configured

@Configuration
public class SecurityHeadersConfig {
    @Bean
    public SecurityFilterChain filterChain(HttpSecurity http) throws Exception {
        http.headers()
            .frameOptions().deny()
            .xssProtection().and()
            .contentSecurityPolicy("default-src 'self'");
        return http.build();
    }
}

[ ] HTTPS Only - Redirect all HTTP to HTTPS
[ ] Secure Cookies - HttpOnly and Secure flags
[ ] Rate Limiting - On all authentication endpoints
[ ] Monitoring - Track failed login attempts
[ ] Backup Authentication - Have a fallback method
[ ] Token Expiration - Short-lived access tokens
[ ] Audit Logging - Log all auth events
[ ] Error Messages - Don't leak information
[ ] Database Indexes - On username/email fields
[ ] Load Testing - Verify system can handle load

Conclusion

Building a production-ready authentication system requires careful consideration of security, scalability, and user experience. The implementation details matter—from proper password hashing to token validation to session management.

Remember: authentication is not a feature you implement once and forget. It requires ongoing maintenance, security updates, and monitoring. Stay informed about new vulnerabilities and best practices.

Next Steps

Implement the authentication system step by step
Add comprehensive logging and monitoring
Conduct security audits regularly
Stay updated with OWASP guidelines
Consider using established libraries like Spring Security

Have questions about authentication implementation? Found a security issue in this guide? Let me know in the comments below or reach out on Twitter.