Among other things (such as permanent subscriptions), Pubsubhubbub 0.4
removed the "sync" verification method. This means that any incoming
PuSH subscription requests that follow the 0.4 spec won't really
_require_that we handle it as a background process, but if we were to
try direct verification of the subscription - and fail - there's no way
we could pick up the ball again. So _essentially_ we require background
processing with retries.
This means we must implement something like the "poorman cron" or
similar, so background processing can be handled
on-demand/on-site-visit. This is how Friendica, Drupal etc. handles it
and is necessary for environments where we can't run separate queue
daemons.
When the poorman-cron-ish thing is implemented, auto-renewal will work
for all users.
PuSH 0.4 spec:
https://pubsubhubbub.googlecode.com/git/pubsubhubbub-core-0.4.html
More on PuSH 0.4 release (incl. breaking changes):
https://groups.google.com/forum/#!msg/pubsubhubbub/7RPlYMds4RI/2mIHQTdV3aoJ
