'Invoked when a new WebSocket requests specific subprotocols.
``subprotocols`` is a list of strings identifying the
subprotocols proposed by the client.  This method may be
overridden to return one of those strings to select it, or
``None`` to not select a subprotocol.  Failure to select a
subprotocol does not automatically abort the connection,
although clients may close the connection if none of their
proposed subprotocols was selected.'

def select_subprotocol(self, subprotocols):

    return None
