As of late, when logging in to Jenkins I get a 503 error from Varnish in return (the green wmerror page, much like our php/wmerror one).
https://integration.wikimedia.org/ci/login?from=%2Fci%2F
It only does that for a successful login though, with a wrong password it just shows the login form again with the relevant error message.
Version: wmf-deployment
Severity: normal