Reply status on socket bridge

Hi,

As I said in a previous PR, congratulation for your nice work, I enjoy your application !
This is a up to date of this feature from master the previous was from branch.2.0.x.

This pull pull request concern only the bridge socket. As far as I understand it, if a person is not authenticated or allow to access to a eventbus address, the message is juste ignore and lost. The client doesn't even know that it request need an authentication. For my understanding, I think It would be interesting to send that information :

 * access_denied : when the user is authenticated but not allow
 * auth_required : when the user is not authenticated
 * auth_error : when we are enable to get user authentication information
 * This a suggestion of implementation because I really don't know if the I reply is a good or the best way.

Best regards,
Maneau