another twitter oAuth cURL access token request that fails

Below is what Ive put together so far and it works :-)

    class Twitauth
    {
      var $key = '';
      var $secret = '';

      var $request_token = "https://twitter.com/oauth/request_token";

    function Twitauth($config)
    {
        $this->key = $config['key']; // consumer key from twitter
        $this->secret = $config['secret']; // secret from twitter
    }

    function getRequestToken()
    {
        // Default params
        $params = array(
            "oauth_version" => "1.0",
            "oauth_nonce" => time(),
            "oauth_timestamp" => time(),
            "oauth_consumer_key" => $this->key,
            "oauth_signature_method" => "HMAC-SHA1"
         );

         // BUILD SIGNATURE
            // encode params keys, values, join and then sort.
            $keys = $this->_urlencode_rfc3986(array_keys($params));
            $values = $this->_urlencode_rfc3986(array_values($params));
            $params = array_combine($keys, $values);
            uksort($params, 'strcmp');

            // convert params to string 
            foreach ($params as $k => $v) {$pairs[] = $this->_urlencode_rfc3986($k).'='.$this->_urlencode_rfc3986($v);}
            $concatenatedParams = implode('&', $pairs);

            // form base string (first key)
            $baseString= "GET&".$this->_urlencode_rfc3986($this->request_token)."&".$this->_urlencode_rfc3986($concatenatedParams);
            // form secret (second key)
            $secret = $this->_urlencode_rfc3986($this->secret)."&";
            // make signature and append to params
            $params['oauth_signature'] = $this->_urlencode_rfc3986(base64_encode(hash_hmac('sha1', $baseString, $secret, TRUE)));

         // BUILD URL
            // Resort
            uksort($params, 'strcmp');
            // convert params to string 
            foreach ($params as $k => $v) {$urlPairs[] = $k."=".$v;}
            $concatenatedUrlParams = implode('&', $urlPairs);
            // form url
            $url = $this->request_token."?".$concatenatedUrlParams;

         // Send to cURL
         print $this->_http($url);          
    }

    function _http($url, $post_data = null)
    {       
        $ch = curl_init();

        curl_setopt($ch, CURLOPT_URL, $url);
        curl_setopt($ch, CURLOPT_CONNECTTIMEOUT, 30);
        curl_setopt($ch, CURLOPT_TIMEOUT, 30);
        curl_setopt($ch, CURLOPT_RETURNTRANSFER, TRUE);
        curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, FALSE);

        if(isset($post_data))
        {
            curl_setopt($ch, CURLOPT_POST, 1);
            curl_setopt($ch, CURLOPT_POSTFIELDS, $post_data);
        }

        $response = curl_exec($ch);
        $this->http_status = curl_getinfo($ch, CURLINFO_HTTP_CODE);
        $this->last_api_call = $url;
        curl_close($ch);

        return $response;
    }

    function _urlencode_rfc3986($input)
    {
        if (is_array($input)) {
            return array_map(array('Twitauth', '_urlencode_rfc3986'), $input);
        }
        else if (is_scalar($input)) {
            return str_replace('+',' ',str_replace('%7E', '~', rawurlencode($input)));
        }
        else{
            return '';
        }
    }
}

not sure if your still looking into this, or if it will work for you, but i had a similar setup and had the same issue. I eventually found i was urlencoding one to many times. Try commenting out this section:

 $keys = $this->_urlencode_rfc3986(array_keys($params));
        $values = $this->_urlencode_rfc3986(array_values($params));
        $params = array_combine($keys, $values);

Worked for me, so maybe it will help.

I'll admit this isn't really an answer, but if you can, use the PECL OAuth package. Rasmus Lerdorf wrote a tutorial on how to use it and it got me around this same issue.