// BAD - Direct object reference
@GetMapping("/users/{id}")
public User getUser(@PathVariable Long id) {
    return userRepository.findById(id);
}

// GOOD - Check authorization
@GetMapping("/users/{id}")
public User getUser(@PathVariable Long id, Authentication auth) {
    User user = userRepository.findById(id);
    if (!user.getId().equals(auth.getPrincipal().getId())) {
        throw new AccessDeniedException("Not authorized");
    }
    return user;
}

// BAD - Weak hashing
String hash = DigestUtils.md5Hex(password);

// GOOD - Strong hashing with salt
BCryptPasswordEncoder encoder = new BCryptPasswordEncoder();
String hash = encoder.encode(password);

// BAD - SQL Injection
String query = "SELECT * FROM users WHERE name = '" + name + "'";

// GOOD - Parameterized query
@Query("SELECT u FROM User u WHERE u.name = :name")
User findByName(@Param("name") String name);

# Spring Security - disable defaults carefully
spring:
  security:
    headers:
      content-security-policy: "default-src 'self'"
      x-frame-options: DENY
      x-content-type-options: nosniff

# Check for vulnerabilities
npm audit
mvn dependency-check:check
pip-audit

// Implement rate limiting
@RateLimiter(name = "login", fallbackMethod = "loginFallback")
public AuthResponse login(LoginRequest request) {
    // ...
}

// Account lockout
if (failedAttempts >= 5) {
    lockAccount(user);
}

// Log security events
log.info("Login attempt", Map.of(
    "user", username,
    "ip", request.getRemoteAddr(),
    "success", authenticated
));

// DON'T log sensitive data
log.info("Password: {}", password);  // NEVER!

// Validate URLs
private boolean isAllowedUrl(String url) {
    URL parsed = new URL(url);
    return allowedHosts.contains(parsed.getHost());
}

@Configuration
public class SecurityConfig {
    @Bean
    public SecurityFilterChain filterChain(HttpSecurity http) {
        return http
            .headers(headers -> headers
                .contentSecurityPolicy(csp -> csp.policyDirectives("default-src 'self'"))
                .frameOptions(frame -> frame.deny())
                .xssProtection(xss -> xss.disable())
            )
            .build();
    }
}