Previously when an access token has expired, the OIDC session was attempted
to be silently refreshed through the use of the OIDCSessionRefreshMiddleware
class.
But silent refresh should be performed at last resort when an OIDC session
just expired. Thus, that diff implements access token renewal directly in
the django auth backend throug the use of a refresh token.
Currently, refresh token have a living period of 30 minutes, meaning a user
can have its authenticated session in idle state during that period.
If he visits a new web page during that idle period, its authenticated
session will then be renewed for another 30 minutes.