Php 单击“登录”按钮后出现致命错误

我可以成功登录，但经过一段时间后，我再次单击登录按钮（通过谷歌帐户登录）后出现此错误

致命错误：未捕获的Google\Service\Exception:{“错误”：{“代码”： 401，“消息”：“请求缺少所需的身份验证 凭据。应为OAuth 2访问令牌、登录cookie或其他有效凭据 身份验证凭据

PHP代码：

if(isset($_SESSION['access_token']))
  $google_client->setAccessToken($_SESSION['access_token']);
else if(isset($_GET['code'])){
  $token = $google_client->fetchAccessTokenWithAuthCode($_GET['code']);
  $_SESSION['access_token'] = $token;
} else{
  header('location: login.php');
  exit();
}



  $oAuth = new Google_Service_Oauth2($google_client);
  $userData = $oAuth->userinfo_v2_me->get();

  $_SESSION['id'] = $userData['id'];
  $_SESSION['email'] = $userData['email'];
  $_SESSION['gender'] = $userData['gender'];
  $_SESSION['picture'] = $userData['picture'];
  $_SESSION['familyName'] = $userData['familyName'];
  $_SESSION['givenName'] = $userData['givenName'];

  header('location: app.php');
  exit();

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我想代币过期了，但我不确定。