Issue with PHP Script to reboot Rackspace server

Question

I have been struggling to write a PHP script that will reboot a server using the 1.6.0 version of the Rackspace API (I can't install Composer on my server needed for 1.7.0). Unfortunately it does not want to recognize my credentials and keeps throwing this error:

Fatal error: Uncaught exception 'OpenCloud\Common\Exceptions\CredentialError' with message 'Unrecognized credential secret' in /home/sandbox/public_html/rackspaceapi/lib/OpenCloud/OpenStack.php:694 Stack trace: #0 /home/sandbox/public_html/rackspaceapi/lib/OpenCloud/Rackspace.php(66): OpenCloud\OpenStack->credentials() #1 /home/sandbox/public_html/rackspaceapi/lib/OpenCloud/OpenStack.php(714): OpenCloud\Rackspace->Credentials() #2 /home/sandbox/public_html/rackspaceapi/lib/OpenCloud/OpenStack.php(591): OpenCloud\OpenStack->authenticate() #3 /home/sandbox/public_html/rackspaceapi/lib/OpenCloud/OpenStack.php(652): OpenCloud\OpenStack->checkExpiration() #4 /home/sandbox/public_html/rackspaceapi/lib/OpenCloud/Common/Service.php(337): OpenCloud\OpenStack->serviceCatalog() #5 /home/sandbox/public_html/rackspaceapi/lib/OpenCloud/Common/Service.php(68): OpenCloud\Common\Service->getEndpoint('compute', 'cloudServersOpe...', 'ORD', 'publicURL') #6 /home/sandbox/public_html/rackspaceapi/lib/OpenCloud/ in /home/sandbox/public_html/rackspaceapi/lib/OpenCloud/OpenStack.php on line 694

Here is my PHP script (I did not include my credentials)

require_once "php-opencloud.php";

// The AUTHURL used for the US was: https://identity.api.rackspacecloud.com/v2.0/

putenv("RAX_USERNAME=$username");
putenv("RAX_API_KEY=$apikey");
putenv("RAX_TENANT_NAME=$tenantname");
putenv("RAX_AUTH_URL=$authurl");

define('USERNAME', $_ENV['RAX_USERNAME']);
define('APIKEY', $_ENV['RAX_API_KEY']);
define('TENANT', $_ENV['RAX_TENANT_NAME']);
define('AUTHURL', 'RAX_AUTH_URL');

$rackspace = new \OpenCloud\Rackspace(AUTHURL,
   array( 'username' => USERNAME,
          'apiKey' => APIKEY ));

$cservers = $rackspace->Compute('cloudServersOpenStack', 'ORD');
$list = $cservers->ServerList();

while($server = $list->Next()) {
      if ($server->name == 'My_Server')
      $server->Reboot('hard');
}

echo "Reboot sequence complete.";

Any help anyone can offer would be greatly appreciated.