Google Calendar API "notFound" 404 error on second action - php

Question

I'm working for this website that allows you to schedule teaching sessions with teachers online on different subjects. We recently added the option for a user to link their google calendar so that every new teaching session they schedule, it's automatically created on their calendar.
This is working great. I've got refresh tokens (offline access) for when the access token expires. So this is all working as it should.
The problem is, when both the teacher and the user have their calendar linked, and my function attempts to create the same event for both, the first one gets created (lets say, for the user), but for when it's time to create the same event for the teacher, it fails with a 404 "notFound", as if it didn't find the calendar.
My guess is that I'm using the same google client object, and you probably can't change the access tokens once you set them. I've tried unset() or $this->gclient = null but it's not working.
I'm using CodeIgniter, so I created a library for google calendar api. In my code, I do something like this:
...
if ($user->hasGoogleCalendar) {
$this->addEventToCalendar($user, $event);
}
if ($teacher->hasGoogleCalendar) {
$this->addEventToCalendar($teacher, $event);
}
...
function addEventToCalendar($user, $event) {
//the constructor for gcalendar creates the google client
$this->load->library("gcalendar");
//this verifies the access token, refreshes if necessary and
//creates the event
$this->gcalendar->addEventToCalendar($user->access_token, $user->calendarId, $event);
}
So this works the first time (for the $user), but then fails (404 notFound) for the $teacher. If I invert the first if statements (so that the teacher is first, then the user), then the teacher gets the event on his/her calendar and the student does not.
So basically the problem is that I can't set a new access_token for the same Google Client, or something like that. I've tried to unload the library and load again but haven't found a way to make it work.
I also tried:
$this->load->library("gcalendar", NULL, "gcalendar1");
$this->load->library("gcalendar", NULL, "gcalendar2");
But it's the same, now I've got 2 different objects $this->gcalendar1 and $this->gcalendar2 but the same error occurs.
For my library I'm using Google Api PHP client
Any ideas?

Answer 1

OK. I analyzed the Google Client class, and it creates a file based cache for the user credentials/data. So the problem was that when a user connected their google calendar account and their data was stored in a file. If another user tried to connect their google calendar, the class wouldn't get this user's credential but instead use the cache file (if it was still valid, I'm guessing time based), but this cache contains files for the first user. So basically user B had a refresh token / access token that belonged to user A, that's why it failed.
For now, I've modified the Google Client class and forced it to not use a cache. I'll do some more research on this because the cache must be there for a reason.
Now it's working like it should!