public function create_credential($recipient_name, $recipient_email, $course_id, $issued_on = null, $expired_on = null, $custom_attributes = null){

		$data = array(
		    "credential" => array(
		    	"group_id" => $course_id,
		        "recipient" => array(
		            "name" => $recipient_name,
		            "email" => $recipient_email
		        ),
		        "issued_on" => $issued_on,
		        "expired_on" => $expired_on,
		        "custom_attributes" => $custom_attributes
		    )
		);

		$client = new \GuzzleHttp\Client();

		$params = array('Authorization' => 'Token token="'.$this->getAPIKey().'"');

		$response = $client->post($this->api_endpoint.'credentials', array(
		    'headers' => $params,
		    'json' => $data
		));

		$result = json_decode($response->getBody());

		return $result;
	}