AnonymousAuthenticationFilter should cache its Supplier<SecurityContext>

[jzheaux]

The Supplier<SecurityContext> in AnonymousAuthenticationFilter gets invoked several times on each request. Essentially, any time getContext is invoked downstream of it. While each call is quick, it seems a bit wasteful.

One way to cache it would be SingletonSupplier

[evgeniycheban]

Hey, @jzheaux I can work on this.