public function fetch_access_token(&$request)
{
$this->get_version($request);
$consumer = $this->get_consumer($request);
// requires authorized request token
$token = $this->get_token($request, $consumer, "request");
$this->check_signature($request, $consumer, $token);
// Rev A change
$verifier = $request->get_parameter('oauth_verifier');
$new_token = $this->data_store->new_access_token($token, $consumer, $verifier);
return $new_token;
}