protected function buildSregParams()
    {
        $params = [];
        /* We always use SREG 1.1, even if the server is advertising only support for 1.0.
        That's because it's fully backwards compatible with 1.0, and some providers
        advertise 1.0 even if they accept only 1.1. One such provider is myopenid.com */
        $params['openid.ns.sreg'] = 'http://openid.net/extensions/sreg/1.1';
        if (!empty($this->requiredAttributes)) {
            $params['openid.sreg.required'] = [];
            foreach ($this->requiredAttributes as $required) {
                if (!isset($this->axToSregMap[$required])) {
                    continue;
                }
                $params['openid.sreg.required'][] = $this->axToSregMap[$required];
            }
            $params['openid.sreg.required'] = implode(',', $params['openid.sreg.required']);
        }

        if (!empty($this->optionalAttributes)) {
            $params['openid.sreg.optional'] = [];
            foreach ($this->optionalAttributes as $optional) {
                if (!isset($this->axToSregMap[$optional])) {
                    continue;
                }
                $params['openid.sreg.optional'][] = $this->axToSregMap[$optional];
            }
            $params['openid.sreg.optional'] = implode(',', $params['openid.sreg.optional']);
        }

        return $params;
    }