Inject @AuthenticationPrincipal when unit testing a Spring REST controller

Question

I am having trouble trying to test a rest endpoint that receives an UserDetails as a parameter annotated with @AuthenticationPrincipal.

Seems like the user instance created in the test scenario is not being used, but an attempt to instantiate using default constructor is made instead: org.springframework.beans.BeanInstantiationException: Failed to instantiate [com.andrucz.app.AppUserDetails]: No default constructor found;

REST endpoint:

@RestController
@RequestMapping("/api/items")
class ItemEndpoint {

    @Autowired
    private ItemService itemService;

    @RequestMapping(path = "/{id}",
                    method = RequestMethod.GET,
                    produces = MediaType.APPLICATION_JSON_UTF8_VALUE)
    public Callable<ItemDto> getItemById(@PathVariable("id") String id, @AuthenticationPrincipal AppUserDetails userDetails) {
        return () -> {
            Item item = itemService.getItemById(id).orElseThrow(() -> new ResourceNotFoundException(id));
            ...
        };
    }
}

Test class:

public class ItemEndpointTests {

    @InjectMocks
    private ItemEndpoint itemEndpoint;

    @Mock
    private ItemService itemService;

    private MockMvc mockMvc;

    @Before
    public void setup() {
        MockitoAnnotations.initMocks(this);
        mockMvc = MockMvcBuilders.standaloneSetup(itemEndpoint)
                .build();
    }

    @Test
    public void findItem() throws Exception {
        when(itemService.getItemById("1")).thenReturn(Optional.of(new Item()));

        mockMvc.perform(get("/api/items/1").with(user(new AppUserDetails(new User()))))
                .andExpect(status().isOk());
    }

}

How can I solve that problem without having to switch to webAppContextSetup? I would like to write tests having total control of service mocks, so I am using standaloneSetup.

Answer 1

This can be done by injection a HandlerMethodArgumentResolver into your Mock MVC context or standalone setup. Assuming your @AuthenticationPrincipal is of type ParticipantDetails:

private HandlerMethodArgumentResolver putAuthenticationPrincipal = new HandlerMethodArgumentResolver() {
    @Override
    public boolean supportsParameter(MethodParameter parameter) {
        return parameter.getParameterType().isAssignableFrom(ParticipantDetails.class);
    }

    @Override
    public Object resolveArgument(MethodParameter parameter, ModelAndViewContainer mavContainer,
            NativeWebRequest webRequest, WebDataBinderFactory binderFactory) throws Exception {
        return new ParticipantDetails(…);
    }
};

This argument resolver can handle the type ParticipantDetails and just creates it out of thin air, but you see you get a lot of context. Later on, this argument resolver is attached to the mock MVC object:

@BeforeMethod
public void beforeMethod() {
    mockMvc = MockMvcBuilders
            .standaloneSetup(…)
            .setCustomArgumentResolvers(putAuthenticationPrincipal)
            .build();
}

This will result in your @AuthenticationPrincipal annotated method arguments to be populated with the details from your resolver.

Answer 2

For some reason Michael Piefel's solution didn't work for me so I came up with another one.

First of all, create abstract configuration class:

@RunWith(SpringRunner.class)
@SpringBootTest
@TestExecutionListeners({
    DependencyInjectionTestExecutionListener.class,
    DirtiesContextTestExecutionListener.class,
    WithSecurityContextTestExecutionListener.class})
public abstract MockMvcTestPrototype {

    @Autowired
    protected WebApplicationContext context;

    protected MockMvc mockMvc;

    protected org.springframework.security.core.userdetails.User loggedUser;

    @Before
    public voivd setUp() {
         mockMvc = MockMvcBuilders
            .webAppContextSetup(context)
            .apply(springSecurity())
            .build();

        loggedUser =  (User)  SecurityContextHolder.getContext().getAuthentication().getPrincipal();
    } 
}

Then you can write tests like this:

public class SomeTestClass extends MockMvcTestPrototype {

    @Test
    @WithUserDetails("someUser@app.com")
    public void someTest() throws Exception {
        mockMvc.
                perform(get("/api/someService")
                    .withUser(user(loggedUser)))
                .andExpect(status().isOk());

    }
}

And @AuthenticationPrincipal should inject your own User class implementation into controller method

public class SomeController {
...
    @RequestMapping(method = POST, value = "/update")
    public String update(UdateDto dto, @AuthenticationPrincipal CurrentUser user) {
        ...
        user.getUser(); // works like a charm!
       ...
    }
}

Answer 3

I know the question is old but for folks still looking, what worked for me to write a Spring Boot test with @AuthenticationPrincipal (and this may not work with all instances), was annotating the test @WithMockUser("testuser1")

@Test
@WithMockUser("testuser1")
public void successfullyMockUser throws Exception {
    mvc.perform(...));
}

Here is a link to the Spring documentation on @WithMockUser

Answer 4

It's not well documented but there's a way to inject the Authentication object as parameter of your MVC method in a standalone MockMvc. If you set the Authentication in the SecurityContextHolder, the filter SecurityContextHolderAwareRequestFilter is usually instantiated by Spring Security and makes the injection of the auth for you.

You simply need to add that filter to your MockMvc setup, like this:

@Before
public void before() throws Exception {
    SecurityContextHolder.getContext().setAuthentication(myAuthentication);
    SecurityContextHolderAwareRequestFilter authInjector = new SecurityContextHolderAwareRequestFilter();
    authInjector.afterPropertiesSet();
    mvc = MockMvcBuilders.standaloneSetup(myController).addFilters(authInjector).build();
}