您不需要authenticate()调用，但是您需要调用refreshTokenWithAssertion()来刷新基础访问令牌.如果您正在使用客户端库发出已签名的请求，则如果基础访问令牌已过期，它将懒惰地为您进行此调用.

You don't need the authenticate() call, but you'll need to call refreshTokenWithAssertion() to refresh the underlying access token. If you are using the client library to make signed requests, it will lazily make this call for you if underlying access token has expired.

API请求刷新access_token很昂贵，并且配额很低，因此您需要缓存access_token.

The API requests to refresh the access_token are expensive, and have a low quota, so you'll want to cache the access_token.

// Set your client id, service account name, and the path to your private key.
// For more information about obtaining these keys, visit:
// https://developers.google.com/console/help/#service_accounts
const CLIENT_ID = 'INSERT_YOUR_CLIENT_ID';
const SERVICE_ACCOUNT_NAME = 'INSERT_YOUR_SERVICE_ACCOUNT_NAME';

// Make sure you keep your key.p12 file in a secure location, and isn't
// readable by others.
const KEY_FILE = '/super/secret/path/to/key.p12';

$client = new Google_Client();
$client->setApplicationName("Google FusionTable Sample");

// Set your cached access token. Remember to store the token in a real database instead of $_SESSION.
session_start();
if (isset($_SESSION['token'])) {
 $client->setAccessToken($_SESSION['token']);
}

$key = file_get_contents(KEY_FILE);
$client->setAssertionCredentials(new Google_AssertionCredentials(
    SERVICE_ACCOUNT_NAME,
    array('https://www.googleapis.com/auth/fusiontables'),
    $key)
);

$client->setClientId(CLIENT_ID);

if ($client->getAuth()->isAccessTokenExpired()) {
  $client->getAuth()->refreshTokenWithAssertion();
}

// Get the json encoded access token.
$token = $client->getAccessToken();