Add Maintenance Mode to Spring (Security) app

I'm looking for a way to implement a Maintenance Mode in my Spring app.

While the app is in Maintenance Mode only users role = MAINTENANCE should be allowed to log in. Everyone else gets redirected to login page.

Right now I just built a Filter:

@Component
public class MaintenanceFilter extends GenericFilterBean {
    @Autowired SettingStore settings;

    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
        if(settingStore.get(MaintenanceMode.KEY).isEnabled()) {
            HttpServletResponse res = (HttpServletResponse) response; 
            res.setStatus(HttpServletResponse.SC_SERVICE_UNAVAILABLE);
        } else {
            chain.doFilter(request, response); 
        }
    }
}

And added it using:

@Override
protected void configure(HttpSecurity http) throws Exception {
    http
        // omitted other stuff
        .addFilterAfter(maintenanceFilter, SwitchUserFilter.class);
}

Because as far as I figured out SwitchUserFilter should be the last filter in Spring Security's filter chain.

Now every request gets canceled with a 503 response. Though there's no way to access the login page.

If I add a redirect to the Filter, this will result in an infinite loop, because access to login page is also denied.

Additionally I can't figure out a nice way to get the current users roles. Or should I just go with SecurityContextHolder ?

---

I'm looking for a way to redirect every user to the login page (maybe with a query param ?maintenance=true) and every user with role = MAINTENANCE can use the application.

So the Filter / Interceptor should behave like:

if(maintenance.isEnabled()) {
    if(currentUser.hasRole(MAINTENANCE)) {
        // this filter does nothing
    } else {
        redirectTo(loginPage?maintenance=true);
    }
}