import org.apache.cassandra.transport.ServerConnection; //导入依赖的package包/类
@Override
public Response execute(QueryState queryState)
{
    try
    {
        SaslAuthenticator authenticator = ((ServerConnection) connection).getAuthenticator();
        byte[] challenge = authenticator.evaluateResponse(token == null ? new byte[0] : token);
        if (authenticator.isComplete())
        {
            AuthenticatedUser user = authenticator.getAuthenticatedUser();
            queryState.getClientState().login(user);
            // authentication is complete, send a ready message to the client
            return new AuthSuccess(challenge);
        }
        else
        {
            return new AuthChallenge(challenge);
        }
    }
    catch (AuthenticationException e)
    {
        return ErrorMessage.fromException(e);
    }
}