public function fetchAccessToken(&$request)
    {
        $this->getVersion($request);
        
        $consumer = $this->getConsumer($request);
        
        // requires authorized request token
        $token = $this->getToken($request, $consumer, "request");
        
        $this->checkSignature($request, $consumer, $token);
        
        // Rev A change
        $verifier = $request->getParameter('oauth_verifier');
        $new_token = $this->data_store->newAccessToken($token, $consumer, $verifier);
        
        return $new_token;
    }