/**
* Generate the oauth_signature parameter
* @return string
*/
public function generateSignature()
{
$keyString = rawurlencode($this->consumer->getSecret()) . '&';
if ($this->accessCredential !== null) {
$keyString .= \rawurlencode($this->accessCredential->getSecret());
}
$baseString = $this->request->getBaseString(self::SIGNATURE_METHOD);
return \base64_encode(hash_hmac('sha1', $baseString, $keyString, true));
}