Allow subclassing of SessionRepositoryMessageInterceptor

[csavory]

This issue could be related to #98

We are currently configuring a WebSocketMessageBroker by extending WebSocketMessageBrokerConfigurationSupport. The reason we are doing this is so we can attach the current user to the Spring Security Context. We do that with these two beans:

    @Bean
    public AbstractSubscribableChannel clientInboundChannel() {
        Executor securityExecutor = new DelegatingSecurityContextExecutor( clientInboundChannelExecutor() );
        ExecutorSubscribableChannel result = new ExecutorSubscribableChannel( securityExecutor );
        result.addInterceptor( securityContextChannelInterceptorAdapter() );
        return result;
    }

    @Bean
    public ChannelInterceptorAdapter securityContextChannelInterceptorAdapter() {
        return new SessionRepositoryMessageInterceptor() {

            @Override
            public Message<?> preSend( Message<?> message, MessageChannel channel ) {
                Authentication auth = (Authentication) SimpMessageHeaderAccessor.getUser( message.getHeaders() );
                SecurityContextHolder.getContext().setAuthentication( auth );
                return super.preSend( message, channel );
            }
        };
    }

I'm trying to follow the examples here: http://docs.spring.io/spring-session/docs/current/reference/html5/guides/websocket.html to integrate Spring session into our application. In order to do that, I would like to change our class definition to:

public class WebSocketConfig extends AbstractSessionWebSocketMessageBrokerConfigurer<ExpiringSession>

and then override this method like this:

    @Override
    public void configureClientInboundChannel(ChannelRegistration registration) {
        registration.setInterceptors(new SessionRepositoryMessageInterceptor<ExpiringSession>(sessionRepository) {

            @Override
            public Message<?> preSend( Message<?> message, MessageChannel channel ) {
                Authentication auth = (Authentication) SimpMessageHeaderAccessor.getUser( message.getHeaders() );
                SecurityContextHolder.getContext().setAuthentication( auth );
                return super.preSend( message, channel );
            }
        });
    }

But I can't because SessionRepositoryMessageInterceptor is final and can't be subclassed. Any chance you can change that class definition?