Spring Security

package com.example.config;

import org.springframework.context.annotation.*;
import org.springframework.security.config.annotation.web.builders.HttpSecurity;
import org.springframework.security.config.annotation.web.configuration.EnableWebSecurity;
import org.springframework.security.crypto.bcrypt.BCryptPasswordEncoder;
import org.springframework.security.crypto.password.PasswordEncoder;
import org.springframework.security.web.SecurityFilterChain;

@Configuration
@EnableWebSecurity
public class SecurityConfig {

    @Bean
    public SecurityFilterChain securityFilterChain(HttpSecurity http) throws Exception {
        http
            // Authorization rules
            .authorizeHttpRequests(auth -> auth
                .requestMatchers("/", "/home", "/register", "/css/**", "/js/**").permitAll()
                .requestMatchers("/admin/**").hasRole("ADMIN")
                .requestMatchers("/api/**").hasAnyRole("USER", "ADMIN")
                .anyRequest().authenticated()
            )
            // Form login
            .formLogin(form -> form
                .loginPage("/login")
                .loginProcessingUrl("/login")
                .defaultSuccessUrl("/dashboard", true)
                .failureUrl("/login?error=true")
                .permitAll()
            )
            // Logout
            .logout(logout -> logout
                .logoutUrl("/logout")
                .logoutSuccessUrl("/login?logout=true")
                .invalidateHttpSession(true)
                .deleteCookies("JSESSIONID")
                .permitAll()
            )
            // HTTP Basic auth (for REST APIs)
            // .httpBasic(Customizer.withDefaults())
            // CSRF protection (disable for REST APIs)
            // .csrf(csrf -> csrf.disable())
            ;

        return http.build();
    }

    @Bean
    public PasswordEncoder passwordEncoder() {
        return new BCryptPasswordEncoder(12); // Strength 12
    }
}

package com.example.security;

import com.example.entity.User;
import com.example.repository.UserRepository;
import org.springframework.security.core.*;
import org.springframework.security.core.authority.SimpleGrantedAuthority;
import org.springframework.security.core.userdetails.*;
import org.springframework.stereotype.Service;
import java.util.*;

@Service
public class UserDetailsServiceImpl implements UserDetailsService {

    private final UserRepository userRepository;

    public UserDetailsServiceImpl(UserRepository userRepository) {
        this.userRepository = userRepository;
    }

    @Override
    public UserDetails loadUserByUsername(String username) throws UsernameNotFoundException {
        User user = userRepository.findByUsername(username)
                .orElseThrow(() -> new UsernameNotFoundException("User not found: " + username));

        // Convert roles to GrantedAuthority
        List<GrantedAuthority> authorities = List.of(
                new SimpleGrantedAuthority("ROLE_" + user.getRole().name())
        );

        return new org.springframework.security.core.userdetails.User(
                user.getUsername(),
                user.getPassword(), // BCrypt hashed password
                authorities
        );
    }
}

// Registration service - hash password before saving
@Service
public class RegistrationService {
    private final UserRepository userRepository;
    private final PasswordEncoder passwordEncoder;

    public RegistrationService(UserRepository userRepository, PasswordEncoder passwordEncoder) {
        this.userRepository = userRepository;
        this.passwordEncoder = passwordEncoder;
    }

    public User register(String username, String email, String rawPassword) {
        User user = new User();
        user.setUsername(username);
        user.setEmail(email);
        user.setPassword(passwordEncoder.encode(rawPassword)); // Hash!
        user.setRole(User.Role.USER);
        return userRepository.save(user);
    }
}

// Enable method security in config:
// @EnableMethodSecurity(prePostEnabled = true)

@Service
public class AdminService {

    // Only ADMIN role can call this
    @PreAuthorize("hasRole('ADMIN')")
    public List<User> getAllUsers() {
        return userRepository.findAll();
    }

    // User can only access their own data
    @PreAuthorize("hasRole('ADMIN') or #username == authentication.name")
    public User getUserProfile(String username) {
        return userRepository.findByUsername(username).orElseThrow();
    }

    // Check after method returns
    @PostAuthorize("returnObject.username == authentication.name or hasRole('ADMIN')")
    public User getUser(Long id) {
        return userRepository.findById(id).orElseThrow();
    }

    // Secure with SpEL expression
    @PreAuthorize("hasRole('ADMIN') and #user.role != 'ADMIN'")
    public void deleteUser(User user) {
        userRepository.delete(user);
    }
}