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.

It

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.