Spring Security Keycloak auth Testing: Mock Authentication object to get access token and userId

I have an application secured by keycloak which works fine. Now I want to write Tests to check my security settings like roles.

This works fine with

@WithMockUser(roles = "customer")

annotion upon my test. In my corresponding Conroller I use the Authentication auth Object to read the keycloak userId and other stuff from the token. Is there a way to mock this??

Controller:

    @PreAuthorize("hasRole('owner') || hasRole('customer') ")
@ApiOperation("Get a list of all products")
@GetMapping(value = "", produces = MediaType.APPLICATION_JSON_VALUE)
public List<Product> findAllProducts(Authentication auth)
{
    SimpleKeycloakAccount account = ((SimpleKeycloakAccount) auth.getDetails());
    KeycloakSecurityContext context = account.getKeycloakSecurityContext();
    AccessToken token = context.getToken();
    String userId = token.getSubject();
    
    return productService.findAll();
}

TEST:

  @Test
    @WithMockUser(roles = "customer")
    void getAllProductsWithEmptyDatabase() throws Exception {
        MvcResult response = mockMvc.perform(get(URL))
                .andExpect(status().isOk())
                .andExpect(MockMvcResultMatchers.content().string(objectMapper.writeValueAsString(Collections.emptyList())))
                .andReturn();

    }