code: public function getAccessToken($forceRefresh = false)
      {
          $cacheKey = $this->getCacheKey();
          $cached = $this->getCache()->fetch($cacheKey);
  
          if (empty($cached) || $forceRefresh) {
              $token = $this->getTokenFormApi();
  
              $this->getCache()->save($cacheKey, $token[$this->tokenSucessKey], $token['expires_in']);
  
              return $token[$this->tokenSucessKey];
          }
  
          return $cached;
      }
docs: Get access token from baidu API.
  
  @param  boolean $forceRefresh
  
  @return string