https://developers.google.com/google-apps/calendar/quickstart/php#step_1_enable_the_api_name Under the notes section of Google Calendar API it says that:
"Authorization information is stored on the file system, so subsequent executions will not prompt for authorization."
The credentials file's location is specified in the CREDENTIALS_PATH variable. use the expandHomeDirectory function to get the exact location.
$credentialsPath = expandHomeDirectory(CREDENTIALS_PATH);
echo $credentialsPath
Mine is is located on: C:\Users\MyUsername\.credentials\calendar-php-quickstart.json
The reason I asked this is that I am having an error saying
Error refreshing the OAuth2 token, message: '{ "error" : "unauthorized_client".....
I deleted the file to become authenticated again.
