502: Make sure user is sent to login screen if session expires

[tmkarlsen]

502 error
The user is often logged out and met with a not-so-informative message.

Screenshot

[emmachughes]

This doesn't seem likely to be related to sessions, and no similar problem happens in the dev environment. This is probably a failure on Vapor's/Lambda's part occurring after the runtime has shut down, and the session having expired at this point is purely coincidental.