private function getAccessTokenFromAuthorizationCode($code) {
    if ($this->getVariable('access_token_uri') && $this->getVariable('client_id') && $this->getVariable('client_secret')) {
      return json_decode($this->makeRequest(
        $this->getVariable('access_token_uri'),
        'POST',
        array(
          'grant_type' => 'authorization_code',
          'client_id' => $this->getVariable('client_id'),
          'client_secret' => $this->getVariable('client_secret'),
          'code' => $code,
          'redirect_uri' => $this->getCurrentUri(),
        )
      ), TRUE);
    }
    return NULL;
  }