PowerMock mock injected Authentication - unit-testing

Question

i am using PowerMockRunner in a spring-boot application for testing. Everything is working but when my controllers actions definition contain someControllerMethod(..., Authentication auth, ...). Then auth is null and therefore some code is not working.
What i tried is to mock Authentication and SecurityContext. Came up with something like this
private void mockSecurity() {
Authentication authentication = mock(Authentication.class);
SecurityContext securityContext = mock(SecurityContext.class);
List<SimpleGrantedAuthority> authorities = Arrays.asList(new SimpleGrantedAuthority("USER"));
User mockedUser = new User("testuser", "passwordtest", authorities);
when(securityContext.getAuthentication()).thenReturn(authentication);
SecurityContextHolder.setContext(securityContext);
when(SecurityContextHolder.getContext().getAuthentication().getDetails()).thenReturn(mockedUser);
when(SecurityContextHolder.getContext().getAuthentication().getName()).thenReturn(mockedUser.getUsername());
}
Now those mocks work, if my code uses SecurityContextHolder.getContext().getAuthentication() method of accessing the authentication, but not for the one automatically injected (probably because it is not yet mocked when the controller mock is created).
Any ideas how to mock the injected Authentication so the code does not need to be changed? spring-security-testand #MockWithUser have the same result.
Relevant parts of the test look like this,
#RunWith(PowerMockRunner.class)
public class UserControllerTest {
#InjectMocks
UserController userController;
#Before
public void setUp() throws Exception {
MockitoAnnotations.initMocks(this);
mockMvc = standaloneSetup(userController).build();
}
#Test
public void getUserDetails() {
mockSecurity();
mockMvc.perform(...).andExpect(...);
}
}
Edit as requested by pvpkiran the controller code
#RequestMapping(...)
public void getDetails(#PathVariable String id, Authentication auth) {
UserDetails loadedDetails = userService.getUserDetails(id);
if (!loadedDetails.getUserId().equals(auth.getName())) {
throw new Exception(...);
}
...
}