Moodle cohort_add_cohort error - php

Question

I'm developing a custom Moodle authentification plugin for Moodle 2.7.
When a user is authenticated I want them to be added to a specific cohort. If that cohort does not exist I need it to be created automatically. I use the user_authenticated_hook() function in my authentification plugin to achieve this.
My code for creating the cohort is this
$data = new stdClass();
$data->name = 'Name string';
$data->idnumber = 'ID string';
$data->description = 'Description string';
$cohortId = cohort_add_cohort($data);
I have included cohort/lib.php in the auth.php file and I have declared the global variables $DB, $CFG and $SESSION at the first line of the user_authenticated_hook() function.
The authentification works without the part about cohorts. But with the cohort part in place authentication fails and I am redirected to the login page.
The page title is changed to "Error" but that is the only error message I get.
What Am I doing wrong? I hope somebody will be able to help me create cohorts and add members.

Answer 1

It might be because the global $USER object doesn't exist yet or hasn't been populated.
Do you have debug switched on in your config.php?
$CFG->debug = 32767;
$CFG->debugdisplay = 1;
It might be better to respond to the user_created event. So if a user is created by another method, they will still be added to the cohort. eg:
Create a local plugin eg:
/local/add_cohorts
Create an events.php
/local/add_cohorts/db/events.php
Which has something like this
$handlers = array (
'user_created' => array (
'handlerfile' => '/local/add_cohorts/lib.php',
'handlerfunction' => 'local_add_cohorts_user_created',
'schedule' => 'instant',
'internal' => 1,
),
);
Then in /local/add_cohorts/lib.php have
function local_add_cohorts_user_created($user) {
// Do your cohort processing here and add the user
// Use $user->id to add to the cohort members
}
Then create a version.php and install the plugin, then the event handler will be registered.
Events api - https://docs.moodle.org/dev/Events_API