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

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

The default implementation always returns L{AUTH_FAILED}.

@param username: the username of the client.
@type username: str
@return: L{AUTH_FAILED} if the authentication fails;
    L{AUTH_SUCCESSFUL} if it succeeds.
@rtype: int