public function getAccessToken(OAuthToken $requestToken, $verifier)
    {
        $request = $this->createRequest('/oauth/access_token', OAuthResponse::FORMAT_STR);
        $request->setOAuthParameter('oauth_verifier', $verifier);
        $this->signRequest($request, $requestToken);

        return $this->createOAuthToken($this->sendRequest($request));
    }