In the failed login cache cleanup loop, the tuple unpacking was using
`login` as the local variable name, silently overwriting the current
user's login with the one retrieved from the expired cache entry.
This caused subsequent backend authentication (e.g. IMAP) to be
attempted with the wrong username, resulting in spurious auth failures
for legitimate users whenever an expired failed-cache entry happened
to be present at the same time.
Rename the loop variable to `login_expired` to avoid shadowing the
outer `login` variable, and fix the associated debug log to reference
`login_expired` instead of the previously incorrect `login_cache`.
Fixes: intermittent authentication failures when _cache_failed contains
expired entries from previous failed login attempts by other users.
Signed-off-by: webmaster <webmaster@jbsky.fr>
e22d5b438f