The following sample is provided “as is” with no warranty or guarantee.

<?php

    /**
     * Define POST URL and also payload
     */
	$username = '';
	$api = '';
	$pass = '';
	$now = actual_time("Y-m-d\TH:i:00",1,time());  // gmdate("Y-m-d\TH:i:00");
	$hash =  custom_hmac('sha1', $pass.'|'.$now, $api, false); // hash_hmac('sha1', $pass.'|'.$now, $api);
	$payload = '<ActivationRequest><Username>'.$username.'</Username><Token>'.$hash.'</Token></ActivationRequest>';
	//echo ($pass.'|'.$now . '<br />');
	//exit(0);
	
    define('XML_PAYLOAD', $payload);
    define('XML_POST_URL', 'https://www.subscriptionbridge.com/Subscriptions/Service2.svc/ActivationRequest');
       
    /**
     * Initialize handle and set options
     */
    $ch = curl_init();
    curl_setopt($ch, CURLOPT_URL, XML_POST_URL);
    curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
    curl_setopt($ch, CURLOPT_TIMEOUT, 4);
    curl_setopt($ch, CURLOPT_POSTFIELDS, XML_PAYLOAD);
    curl_setopt($ch, CURLOPT_HTTPHEADER, array('Content-type: text/xml'));
    
	//WARNING: this would prevent curl from detecting a 'man in the middle' attack
   	curl_setopt ($ch, CURLOPT_SSL_VERIFYHOST, 0);
	curl_setopt ($ch, CURLOPT_SSL_VERIFYPEER, 0); 
    
	/**
     * Execute the request and also time the transaction
     */
    $start = array_sum(explode(' ', microtime()));
    $result = curl_exec($ch);
    $stop = array_sum(explode(' ', microtime()));
    $totalTime = $stop - $start;
   
    /**
     * Check for errors
     */
    if ( curl_errno($ch) ) {
        $resultMsg = 'ERROR -> ' . curl_errno($ch) . ': ' . curl_error($ch);
    } else {
        $returnCode = (int)curl_getinfo($ch, CURLINFO_HTTP_CODE);
        switch($returnCode){
            case 404:
                $resultMsg = 'ERROR -> 404 Not Found';
                break;
            case 200:
                break;
            default:
                $resultMsg = 'HTTP ERROR -> ' . $returnCode;
                break;
        }
    }
   
    /**
     * Close the handle
     */
    curl_close($ch);
   
    /**
     * Output the results and time
     */
    echo 'Total time for request: ' . $totalTime . "\n";
    echo $result;  
   
    /**
     * Exit the script
     */
    exit(0);
	
	function actual_time($format,$offset,$timestamp){
	   //Offset is in hours from gmt, including a - sign if applicable.
	   //So lets turn offset into seconds
	   $offset = $offset*60*60;
	   $timestamp = $timestamp + $offset;
		//Remember, adding a negative is still subtraction ;)
	   return gmdate($format,$timestamp);
	}
	
	function custom_hmac($algo, $data, $key, $raw_output)
	{
		$algo = strtolower($algo);
		$pack = 'H'.strlen($algo('test'));
		$size = 64;
		$opad = str_repeat(chr(0x5C), $size);
		$ipad = str_repeat(chr(0x36), $size);
	
		if (strlen($key) > $size) {
			$key = str_pad(pack($pack, $algo($key)), $size, chr(0x00));
		} else {
			$key = str_pad($key, $size, chr(0x00));
		}
	
		for ($i = 0; $i < strlen($key) - 1; $i++) {
			$opad[$i] = $opad[$i] ^ $key[$i];
			$ipad[$i] = $ipad[$i] ^ $key[$i];
		}
	
		$output = $algo($opad.pack($pack, $algo($ipad.$data)));
	
		return ($raw_output) ? pack($pack, $output) : $output;
	}

?>