问mockmvc:使用mockMvc测试控制器时，如何处理认证参数？

EN

@PostMapping("/xx")
public String xx(Authentication auth){
    String userId = (String)auth.getPrincipal();
    ....
}

public class MyControllerTest{
    @Autowired
    private XxController xxController;

    private MockMvc mockMvc;

    @Before
    public void setUp() {
        mockMvc = MockMvcBuilders.standaloneSetup(xxController).build();
    }

    @Test
    public void xxtestMethod() throws Exception {

    MvcResult mvcResult = mockMvc.perform(MockMvcRequestBuilders.post(/xx))
            .andExpect(MockMvcResultMatchers.status().isOk())
            .andDo(MockMvcResultHandlers.print())
            .andReturn();
    }
}