StartExam

    function start_exam_auth($verb = 'GET', $canonical_path = '', $content_length = 0) {
        $result = $this->start_exam_id . ":";
        $StringToSign = strtoupper($verb) . ' ' . strtolower($canonical_path) . ' ' . str_replace('+0000','GMT',gmdate(DATE_RFC1123)) .' '. $content_length;
        $hash = hash_hmac('sha256',  utf8_encode($StringToSign), $this->start_exam_secret_key, true);
        $Signature = $result . base64_encode($hash);
        return $Signature;
    }

    function start_exam_register() {
        $method = "POST";
        $xml = '<?xml version="1.0" encoding="utf-16"?>
                    <RegisterParticipantsQuery xmlns="https://api.startexam.com/v1/xml">
                        <Center>at19629</Center>
                        <ValidFrom>2015-01-16T00:00:00Z</ValidFrom>
                        <ValidTill>2016-01-31T23:59:59Z</ValidTill>
                        <Test>2eca1305-a99f-4f43-bdb9-ba93e5ca86af</Test>
                        <Participant>
                            <Data key="FirstName" value="John" />
                            <Data key="LastName" value="Lennon" />
                            <Data key="Email" value="lennon@gmail.com" />
                            <Data key="f1094d46-fe61-49fc-89a7-d534e9a2c013" value="000000000" />
                        </Participant>
                        <Participant>
                            <Data key="FirstName" value="Paul" />
                            <Data key="LastName" value="McCartney" />
                            <Data key="Email" value="paulmccartney@hotmail.com" />
                            <Data key="f1094d46-fe61-49fc-89a7-d534e9a2c013" value="999999999" />
                        </Participant>
                    </RegisterParticipantsQuery>';
        //----------------------
        $opts = array(
            'http' => array(
                'Method' => $method,
                'Header' => 'Authorization: SharedKey '.$this->start_exam_auth($method, '/v1/participants', strlen($xml)). "\r\n".
                            'Accept: application/json; charset=utf-8'. "\r\n".
                            'Content-Length: '.strlen($xml). "\r\n".
                            'Date: '.str_replace('+0000','GMT',gmdate(DATE_RFC1123)). "\r\n".
                            'Host: api.startexam.com',
                'Content' => $xml
            )
        );

        //print_r($opts);
        //exit();
        $context = stream_context_create($opts);
        $result = file_get_contents("https://api.startexam.com/v1/participants", false, $context);
        return $result;
    }