This changes the "Sign out" link on Studio to point to Studio's own logout
view, which clears the session and then redirects to LMS's logout page. The
LMS logout page then skips loading the Studio logout because it is seen in
the Referer header.
This change also brings Studio better into line with how other IDAs perform
their logouts.
Background:
After the rollout of Studio OAuth, logouts initiated on Studio failed to
actually log out Studio (but all other IDAs were logged out). This was
because the LMS logout view loads the logout pages of other IDAs but skips
any that is a *prefix* match on the Referer header, and browsers now often
send a truncated version of the Referer for privacy. Therefore, Studio was
always skipped when coming from Studio.
The fix is to make sure that Studio has already performed its logout by the
time the LMS logout page is loaded.
One wrinkle here is that the LMS logout view is activated by `/logout`, but
the correct logout view (provided by auth_backends) is activated by
`/logout/` -- with a trailing slash. This is fragile and unfortunate, but
can be cleaned up when we later remove other leftovers of Studio's previous
ability to handle logistration.
ref: ARCHBOM-1897
0c164ad4c2
