/**
  * Build signature
  *
  * @param String $baseString - base string
  * @param OAuthConsumer $consumer - consumer
  * @param OAuthToken $token - token
  * @return String
  */
 public function build($baseString, $consumer, $token)
 {
     $keyParts = array($consumer->getSecret(), $token ? $token->getSecret() : '');
     $keyParts = OAuthUtils::urlEncodeRfc3986($keyParts);
     $key = implode('&', $keyParts);
     return base64_encode(hash_hmac('sha1', $baseString, $key, true));
 }