clearSession invalidated the session-store record and zeroed both
session/CSRF cookies on the client side, but never deleted the
matching entry from the CSRF store. The orphaned record stuck around
for up to 4 hours (CSRF TTL) after every logout. Not exploitable —
the session itself was gone, so the stale CSRF entry could not be
used — but the asymmetry was real: InvalidateUserSessions (password
change) and InvalidateOldSessionFromRequest (re-login) both already
called DeleteCSRFToken, and logout was the missing path.
Add the same call in clearSession alongside InvalidateSession.
Regression test TestClearSession_DeletesServerSideCSRFToken sets up a
real session + CSRF token pair, calls clearSession with a request
carrying the session cookie, and asserts the CSRF token no longer
validates against the session ID afterward.
rcourtman
1118e09fcd