Then latter i can check if the access token is expired if so i refresh it

 if ($client->isAccessTokenExpired()) {             
            $client->fetchAccessTokenWithRefreshToken($client->getRefreshToken());
            $client->setAccessToken($client->getAccessToken());   
            $_SESSION['access_token'] = $client->getAccessToken();                
        }       

oauth2callback.php

    require_once __DIR__ . '/vendor/autoload.php';
    require_once __DIR__ . '/Oauth2Authentication.php';
    
    // Start a session to persist credentials.
    session_start();
    
    // Handle authorization flow from the server.
    if (! isset($_GET['code'])) {
        $client = buildClient();
        $auth_url = $client->createAuthUrl();
        header('Location: ' . filter_var($auth_url, FILTER_SANITIZE_URL));
    } else {
        $client = buildClient();
        $client->authenticate($_GET['code']); // Exchange the authencation code for a refresh token and access token.
        // Add access token and refresh token to seession.
        $_SESSION['access_token'] = $client->getAccessToken();
        $_SESSION['refresh_token'] = $client->getRefreshToken();    
        //Redirect back to main script
        $redirect_uri = str_replace("oauth2callback.php",$_SESSION['mainScript'],$client->getRedirectUri());    
        header('Location: ' . filter_var($redirect_uri, FILTER_SANITIZE_URL));
    }

身份验证.php

require_once __DIR__ . '/vendor/autoload.php';
/**
 * Gets the Google client refreshing auth if needed.
 * Documentation: https://developers.google.com/identity/protocols/OAuth2
 * Initializes a client object.
 * @return A google client object.
 */
function getGoogleClient() {
    $client = getOauth2Client();

    // Refresh the token if it's expired.
    if ($client->isAccessTokenExpired()) {
        $client->fetchAccessTokenWithRefreshToken($client->getRefreshToken());
        file_put_contents($credentialsPath, json_encode($client->getAccessToken()));
    }
return $client;
}

/**
 * Builds the Google client object.
 * Documentation: https://developers.google.com/identity/protocols/OAuth2
 * Scopes will need to be changed depending upon the API's being accessed.
 * Example:  array(Google_Service_Analytics::ANALYTICS_READONLY, Google_Service_Analytics::ANALYTICS)
 * List of Google Scopes: https://developers.google.com/identity/protocols/googlescopes
 * @return A google client object.
 */
function buildClient(){
    
    $client = new Google_Client();
    $client->setAccessType("offline");        // offline access.  Will result in a refresh token
    $client->setIncludeGrantedScopes(true);   // incremental auth
    $client->setAuthConfig(__DIR__ . '/client_secrets.json');
    $client->addScope([YOUR SCOPES HERE]);
    $client->setRedirectUri(getRedirectUri());  
    return $client;
}

/**
 * Builds the redirect uri.
 * Documentation: https://developers.google.com/api-client-library/python/auth/installed-app#choosingredirecturi
 * Hostname and current server path are needed to redirect to oauth2callback.php
 * @return A redirect uri.
 */
function getRedirectUri(){

    //Building Redirect URI
    $url = $_SERVER['REQUEST_URI'];                    //returns the current URL
    if(strrpos($url, '?') > 0)
        $url = substr($url, 0, strrpos($url, '?') );  // Removing any parameters.
    $folder = substr($url, 0, strrpos($url, '/') );   // Removeing current file.
    return (isset($_SERVER['HTTPS']) ? "https" : "http") . '://' . $_SERVER['HTTP_HOST'] . $folder. '/oauth2callback.php';
}


/**
 * Authenticating to Google using Oauth2
 * Documentation:  https://developers.google.com/identity/protocols/OAuth2
 * Returns a Google client with refresh token and access tokens set. 
 *  If not authencated then we will redirect to request authencation.
 * @return A google client object.
 */
function getOauth2Client() {
    try {
        
        $client = buildClient();
        
        // Set the refresh token on the client. 
        if (isset($_SESSION['refresh_token']) && $_SESSION['refresh_token']) {
            $client->refreshToken($_SESSION['refresh_token']);
        }
        
        // If the user has already authorized this app then get an access token
        // else redirect to ask the user to authorize access to Google Analytics.
        if (isset($_SESSION['access_token']) && $_SESSION['access_token']) {
            
            // Set the access token on the client.
            $client->setAccessToken($_SESSION['access_token']);                 
            
            // Refresh the access token if it's expired.
            if ($client->isAccessTokenExpired()) {              
                $client->fetchAccessTokenWithRefreshToken($client->getRefreshToken());
                $client->setAccessToken($client->getAccessToken()); 
                $_SESSION['access_token'] = $client->getAccessToken();              
            }           
            return $client; 
        } else {
            // We do not have access request access.
            header('Location: ' . filter_var( $client->getRedirectUri(), FILTER_SANITIZE_URL));
        }
    } catch (Exception $e) {
        print "An error occurred: " . $e->getMessage();
    }
}
?>

服务帐号代码

凭证文件不同，请勿混淆.

function getServiceAccountClient() {
try {   
    // Create and configure a new client object.        
    $client = new Google_Client();
    $client->useApplicationDefaultCredentials();
    $client->addScope([YOUR SCOPES HERE]);
    return $client;
} catch (Exception $e) {
    print "An error occurred: " . $e->getMessage();
}