# Caching credentials
  
  You can speed up your API operations by caching your credentials in a (semi-)permanent location, such as your
  DB or local filesystem. This enable subsequent requests to access a shared resource, instead of repetitively having to
  re-authenticate on every thread of execution.
  
  Tokens are valid for 24 hours, so you can effectively re-use the same cached value for that period. If you try to use
  a cached version that has expired, an authentication request will be made.
  
  ## Filesystem example
  
  In this example, credentials will be saved to a file in the local filesystem. Be sure to exclude it from your VCS.
  
  ```php
  use OpenCloud\Rackspace;
  
  $client = new Rackspace(Rackspace::US_IDENTITY_ENDPOINT, array(
      'username' => 'foo',
      'apiKey'   => 'bar'
  ));
  
  $cacheFile = __DIR__ . '/.opencloud_token';
  
  // If the cache file exists, try importing it into the client
  if (file_exists($cacheFile)) {
      $data = unserialize(file_get_contents($cacheFile));
      $client->importCredentials($data);
  }
  
  $token = $client->getTokenObject();
  
  // If no token exists, or the current token is expired, re-authenticate and save the new token to disk
  if (!$token || ($token && $token->hasExpired())) {
      $client->authenticate();
      file_put_contents($cacheFile, serialize($client->exportCredentials()));
  }
  ```
  
  In tests, the above code shaved about 1-2s off the execution time.