public class CustomAuthentication implements AuthenticationProvider {

    @Autowired
    private UserRepository userRepository;



    @Override
    public Authentication authenticate(Authentication authentication) throws AuthenticationException {
        String userLogin = authentication.getName();
        String password = authentication.getCredentials().toString();

        User user = userRepository.findOneByLogin(userLogin).orElse(null);
        if (userLogin.equalsIgnoreCase("test") && password.equals("test")) {           // replace your custom code here for custom authentication
            return new UsernamePasswordAuthenticationToken
                    (userLogin, password, Collections.emptyList());
        } else {
            throw new BadCredentialsException("External system authentication failed");
        }
    }

    @Override
    public boolean supports(Class<?> authentication) {
        return true;
    }
}

@Repository("userRepository")
    public interface UserRepository extends CrudRepository<User, Long> {
        @Query(value = "SELECT * FROM user u WHERE u.login = ? ", nativeQuery = true)
        Optional<User> findOneByLogin(String login);
        Optional<User> findOneById(long id);
        List<User> findAll();
    }