PHPのcurl関数を用いてTwitterAPIのリクエストトークンを取得

PHPのcurl関数を用いてTwitterAPIのリクエストトークン
以下のコードで取得する際

"{"errors":[{"code":215,"message":"Bad Authentication data."}]}" 

が返って来ます。
理由がわからず困っております。お願いします

$params = array(
    'oauth_callback' => '' ,
    'oauth_consumer_key' => '' ,
    'oauth_signature_method' => 'HMAC-SHA1' ,
    'oauth_timestamp' => mktime() ,
    'oauth_nonce' => md5(uniqid(rand(), true)) ,
    'oauth_version' => '1.0'
);

  $url =array(
    'request_url' => 'https://api.twitter.com/oauth/request_token' ,
    'access_url' => 'https://api.twitter.com/oauth/access_token' ,
);

  $key = array(
    'consumer_key' => '' ,
    'consumer_secret' => '' ,
    'access_token_secret' => '',
  );

  $request_method = 'POST';
  $request_url = $url['request_url'];
  $signature_key = rawUrlEncode($key['consumer_secret']) . '&' . rawUrlEncode($key['access_token_secret']);

  foreach ($params as $key => $value) {
    if ($key !== 'oauth_callback') {
      $params[$key] = rawUrlEncode($value);
    }else {
      continue;
    }
  }
  ksort($params);

  $request_params = http_build_query($params , ' ' , '&');
  $encode_url = array(
    'request_params' => rawUrlEncode($request_params) ,
    'encoded_request_method' =>rawUrlEncode($request_method) ,
    'encoded_request_url' => rawUrlEncode($request_url)
  );
$signature_data = $encode_url['encoded_request_method'] . '&' . $encode_url['encoded_request_url'] . '&' . $request_params;

$hash = hash_hmac('sha1' , $signature_data , $signature_key , TRUE);
$signature = base64_encode($hash);

$params['oauth_signature'] = $signature;

  $header_params = http_build_query($params , ' ' , ',');
  $context = array(
    'http' => array(
      'method' => $request_method,
      'header' => array(
        'Authorization: OAuth' . $header_params ,
      ),
    )
  );

  $curl = curl_init();
  curl_setopt($curl , CURLOPT_URL , $request_url);
  curl_setopt($curl , CURLOPT_HEADER , 1);
  curl_setopt($curl , CURLOPT_CUSTOMREQUEST , $context['http']['method']);
  curl_setopt($curl ,  CURLOPT_SSL_VERIFYPEER , false);
  curl_setopt($curl ,  CURLOPT_RETURNTRANSFER , true);
  curl_setopt($curl ,  CURLOPT_HTTPHEADER ,  $context['http']['header']));
  curl_setopt($curl ,  CURLOPT_TIMEOUT , 5);
  $post1 = curl_exec($curl);
  $post2 = curl_getinfo($curl);
  curl_close($curl);

  $params = $params;
  $response = substr($post1 , $post2['header_size']);
  $header = substr($post1 , 0 , $post2['header_size']);

  echo $header;
?>