Handle next() call in oauth login

[sethvincent]

We should look into how to handle this:

osm-teams/app/oauth/login.js

Line 12 in d54c354

if (!challenge) return next()

[kamicut]

Recapping conversation: next() doesn't go anywhere, so it's undefined behavior. We could use this opportunity to create test fixtures to simulate hydra (the token generator) failing and have the app figure out what to do