@Controller

public class PersonController {

    @Autowired
    private PersonRepository personRepository;

    @RequestMapping(value="/authenticate", method = RequestMethod.POST)
    public ResponseEntity<String> authenticate(@RequestBody Person person) {

        Person authenticated = personRepository.findByUsernameAndPassword(person.getUsername(), person.getPassword());

        if (authenticated == null) {
            return new ResponseEntity<>("UNKNOWN", HttpStatus.UNAUTHORIZED);
        }
        return new ResponseEntity<>(authenticated.getName(), HttpStatus.OK);

    }
}
public interface PersonRepository extends JpaRepository<Person, Long> {

    @RestResource(exported = false)
    @Override
    public void delete(Long id);
    public Person findByUsernameAndPassword(String username, String password);

}