public function getWwwAuthenticateHeader()
    {
        $wwwAuthenticateHeader = 'Hawk';

        foreach ($this->wwwAuthenticateHeaderAttributes as $key => $value) {
            $value = $value === null ? '': $value;

            $wwwAuthenticateHeader .= " $key=\"$value\",";
        }

        if ($this->message) {
            $wwwAuthenticateHeader .= " error=\"$this->message\"";
        } else {
            // Remove comma at the end
            $wwwAuthenticateHeader = rtrim($wwwAuthenticateHeader, ',');
        }

        return $wwwAuthenticateHeader;
    }