public <T> ResponseEntity<T> login(ParameterizedTypeReference<T> responseType) {
        return testRestTemplate.exchange(API_1_0_LOGIN, HttpMethod.POST, null, responseType);
    }

public static User createValidUser() {
        User user = new User();
        user.setUserId(1L);
        user.setUsername("test-user");
        user.setDisplayName("test-display");
        user.setPassword("P4assword");
        return user;
    }

 @Test
 public void postLogin_withValidCredentials_receiveLoggedInUserId() {
        User inDB = userService.save(createValidUser());
        authenticate();
        ResponseEntity<Map<String, Object>> response = login(new ParameterizedTypeReference<>() {});
        Map<String, Object> body = response.getBody();

        Integer id = (Integer) body.get("id");
        assertThat(id).isEqualTo(inDB.getUserId());
    }


    @PostMapping
    public Map<String, Object> handleLogin() {
        User loggedInUser = (User) SecurityContextHolder.getContext().getAuthentication().getPrincipal();
        return Collections.singletonMap("id", loggedInUser.getUserId());
    }