def check_auth_none(self, username):
return AUTH_FAILED<EOL>
Determine if a client may open channels with no (further)
authentication.

Return ``AUTH_FAILED`` if the client must authenticate, or
``AUTH_SUCCESSFUL`` if it's okay for the client to not
authenticate.

The default implementation always returns ``AUTH_FAILED``.

:param str username: the username of the client.
:return:
    ``AUTH_FAILED`` if the authentication fails; ``AUTH_SUCCESSFUL`` if
    it succeeds.
:rtype: int