I've got the same issue, we a site (wordpress) which has 35,000 users logging in and out via steam since September 2015. Only in the last 6-7 days has this been an issue and we're getting a LOT of requests from users saying they can't login.
OneAl…
Yes, that does answer the question and it's probably a good one from the looks of it.
I don't have Curl installed on the server atm but I can sort that out then give this a test.