I’m currently rebuilding a PHP 5.6 application into Java, which is expected to go beyond June. Until then, I need to ensure that push notifications continue to be sent by migrating them.

The problem is that the ‘Google App Engine PHP 5 Standard Environment Document’, which explains user authentication services using Google OAuth2, terminated on January 30. I have two questions about this:

1. How can I receive Google OAuth2 tokens with PHP version 5.6?
2. How does the sending method using the FCM HTTP v1 protocol work with PHP 5.6?

Through gpt, I received the following source. However, I am not sure of how to get $refreshToken, and there is uncertainty about whether this source works correctly.

function get_access_token($clientId, $clientSecret, $refreshToken) {
    $url = 'https://accounts.google.com/o/oauth2/token';
    $data = [
        'client_id' => $clientId,
        'client_secret' => $clientSecret,
        'refresh_token' => $refreshToken,
        'grant_type' => 'refresh_token',
    ];

    $ch = curl_init();
    curl_setopt($ch, CURLOPT_URL, $url);
    curl_setopt($ch, CURLOPT_POST, true);
    curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
    curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false);
    curl_setopt($ch, CURLOPT_POSTFIELDS, http_build_query($data));

    $result = curl_exec($ch);
    curl_close($ch);

    $result = json_decode($result, true);

    if(array_key_exists('access_token', $result)) {
        return $result['access_token'];
    } else {
        return null;
    }
}

function send_notification_common($tokens, $message) {
    $clientId = 'MyClientId';
    $clientSecret = 'MyClientSecret';

    $url = 'https://fcm.googleapis.com/v1/projects/gymgym-4ecef/messages:send';
    $fields = array(
        'message' => array(
            'token' => $tokens,
            'notification' => $message,
            'data' => $message
        )
    );
    $headers = array(
        'Authorization: Bearer ' . get_access_token($clientId, $clientSecret, $refreshToken),
        'Content-Type: application/json'
    );

    $ch = curl_init();
    curl_setopt($ch, CURLOPT_URL, $url);
    curl_setopt($ch, CURLOPT_POST, true);
    curl_setopt($ch, CURLOPT_HTTPHEADER, $headers);
    curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
    curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, 0);
    curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false);
    curl_setopt($ch, CURLOPT_POSTFIELDS, json_encode($fields));
    $result = curl_exec($ch);
    if ($result === FALSE) {
        die('Curl failed: ' . curl_error($ch));
    }
    curl_close($ch);
    return $result;
}

Could you tell me how to use this code or if there are other methods?

Thank you.

1. Visit the Google Cloud Console.
2. From the project drop-down at the top, create a new project or select an existing one.
3. From the sidebar menu, select “APIs & Services” > “Credentials”.
4. On the “Credentials” page, click “Create Credentials” > “OAuth client ID”.
5. In the “Create OAuth client” screen, select “Web application” and click “Create”.
6. In the next screen, you can see the client ID ($clientId) and client secret ($clientSecret).

$refreshToken
https://accounts.google.com/o/oauth2/auth?redirect_uri=http://localhost&response_type=code&client_id=myClientId&access_type=offline&prompt=consent&scope=https://www.googleapis.com/auth/cloud-platform

After this, it was moved to the url http://localhost/?code=4/0adLIrYehJFAe5XYrzWOAvX9gdkRyB5gJk6pyAeXpgUSMbgV8eLCMjhDHHxN-85_YUyx5SA&scope=https://www.googleapis.com/auth/cloud-platform.

I’m not sure what I should do after this