[Security] Custom authentication provider imports removed exception

[norkunas]

While fixing another docs issue I've noticed that this example imports removed Symfony\Component\Security\Core\Exception\NonceExpiredException since v4.
How should we proceed fixing this?

[xabbuh]

A quick fix could be just to throw an instance of the generic AuthenticationException and add a comment above it that in a real world application it would make sense to throw a custom exception extending the generic one.