each request should have valid ID Token

Each incoming request is expected to have signed non-expired JSON Web Token, containing information about user (sub), matching edx-notes client id (to be set in provider's database) and signed with edx-notes client secret (the same). 

https://openedx.atlassian.net/browse/TNL-780
Why just do not use `request.user`? For example, https://github.com/tomchristie/django-rest-framework/blob/master/rest_framework/permissions.py#L47