public function set($variableName, $value)
    {
        $authorizedSetters = array(
            'clientRef',
            'phoneNumber',
            'codeLength',
            'codeType',
            'caseSensitive',
            'callbackUrl',
            'senderId',
            'messageTemplate'
        );

        if (in_array($variableName, $authorizedSetters)) {
            $name = 'set' . ucfirst($variableName);
            $this->$name($value);
        } else {
            throw new \Exception('No setter for ' . $variableName . '.');
        }

        return $this;
    }