The OnCanSaveNewEntity and OnCanSaveExistingEntity are called before the entity is save. It means you call entity.Save, then these methods are internally called from your auditor and if the save is not authorized, no save action occurs (it's ignored).
If you want something like ...
bool authorized = myAuthorizer.Authorize()
... the answer is no, there is no such method in the Authorizer. You can add it to your own Authorizer class.