Change third party auth login failure code to a 401, to detect authentication
success with no linked account.
If already authenticated, redirect immediately to the dashboard.
Use "Location" header correctly for 302 redirects from student views.
Add utility functions for simulating a running third-party auth pipeline.
Add a utility function for checking whether third party auth is enabled.
Respect default values sent by the server
Expose a new endpoint to query a list of users based on a
role name (Moderator, Student, etc.) and a course_id.
This will initially be used by the notifier to send daily digest
messages to forum moderators.
The endpoint includes the key of the desired preference in the URL and
returns the list of users for whom the preference is set (regardless of
the value).
