Unit testing with Spring Security

Just do it the usual way and then insert it using SecurityContextHolder.setContext() in your test class, for example:

Controller:

Authentication a = SecurityContextHolder.getContext().getAuthentication();

Test:

Authentication authentication = Mockito.mock(Authentication.class);
// Mockito.whens() for your authorization object
SecurityContext securityContext = Mockito.mock(SecurityContext.class);
Mockito.when(securityContext.getAuthentication()).thenReturn(authentication);
SecurityContextHolder.setContext(securityContext);

The problem is that Spring Security does not make the Authentication object available as a bean in the container, so there is no way to easily inject or autowire it out of the box.

Before we started to use Spring Security, we would create a session-scoped bean in the container to store the Principal, inject this into an "AuthenticationService" (singleton) and then inject this bean into other services that needed knowledge of the current Principal.

If you are implementing your own authentication service, you could basically do the same thing: create a session-scoped bean with a "principal" property, inject this into your authentication service, have the auth service set the property on successful auth, and then make the auth service available to other beans as you need it.

I wouldn't feel too bad about using SecurityContextHolder. though. I know that it's a static / Singleton and that Spring discourages using such things but their implementation takes care to behave appropriately depending on the environment: session-scoped in a Servlet container, thread-scoped in a JUnit test, etc. The real limiting factor of a Singleton is when it provides an implementation that is inflexible to different environments.

Without answering the question about how to create and inject Authentication objects, Spring Security 4.0 provides some welcome alternatives when it comes to testing. The @WithMockUser annotation enables the developer to specify a mock user (with optional authorities, username, password and roles) in a neat way:

@Test
@WithMockUser(username = "admin", authorities = { "ADMIN", "USER" })
public void getMessageWithMockUserCustomAuthorities() {
    String message = messageService.getMessage();
    ...
}

There is also the option to use @WithUserDetails to emulate a UserDetails returned from the UserDetailsService, e.g.

@Test
@WithUserDetails("customUsername")
public void getMessageWithUserDetailsCustomUsername() {
    String message = messageService.getMessage();
    ...
}

More details can be found in the @WithMockUser and the @WithUserDetails chapters in the Spring Security reference docs (from which the above examples were copied)

You are quite right to be concerned - static method calls are particularly problematic for unit testing as you cannot easily mock your dependencies. What I am going to show you is how to let the Spring IoC container do the dirty work for you, leaving you with neat, testable code. SecurityContextHolder is a framework class and while it may be ok for your low-level security code to be tied to it, you probably want to expose a neater interface to your UI components (i.e. controllers).

cliff.meyers mentioned one way around it - create your own "principal" type and inject an instance into consumers. The Spring <aop:scoped-proxy/> tag introduced in 2.x combined with a request scope bean definition, and the factory-method support may be the ticket to the most readable code.

It could work like following:

public class MyUserDetails implements UserDetails {
    // this is your custom UserDetails implementation to serve as a principal
    // implement the Spring methods and add your own methods as appropriate
}

public class MyUserHolder {
    public static MyUserDetails getUserDetails() {
        Authentication a = SecurityContextHolder.getContext().getAuthentication();
        if (a == null) {
            return null;
        } else {
            return (MyUserDetails) a.getPrincipal();
        }
    }
}

public class MyUserAwareController {        
    MyUserDetails currentUser;

    public void setCurrentUser(MyUserDetails currentUser) { 
        this.currentUser = currentUser;
    }

    // controller code
}

Nothing complicated so far, right? In fact you probably had to do most of this already. Next, in your bean context define a request-scoped bean to hold the principal:

<bean id="userDetails" class="MyUserHolder" factory-method="getUserDetails" scope="request">
    <aop:scoped-proxy/>
</bean>

<bean id="controller" class="MyUserAwareController">
    <property name="currentUser" ref="userDetails"/>
    <!-- other props -->
</bean>

Thanks to the magic of the aop:scoped-proxy tag, the static method getUserDetails will be called every time a new HTTP request comes in and any references to the currentUser property will be resolved correctly. Now unit testing becomes trivial:

protected void setUp() {
    // existing init code

    MyUserDetails user = new MyUserDetails();
    // set up user as you wish
    controller.setCurrentUser(user);
}

Hope this helps!