private function buildAuthorizationHeader($oauth) 
    {
        $return = 'Authorization: OAuth ';
        $values = array();
        
        foreach($oauth as $key => $value)
        {
            $values[] = "$key=\"" . rawurlencode($value) . "\"";
        }
        
        $return .= implode(', ', $values);
        return $return;
    }