bug: Facebook OAuth login not working

[dmetzner]

Description

Facebook OAuth login is currently not functional. Clicking the Facebook login button fails to authenticate users.

Steps to reproduce

1. Go to /app/login
2. Click the Facebook icon under "Or you can join with"
3. Authentication fails

Expected behavior

Users should be able to log in via their Facebook account.

Temporary workaround

Facebook login button is hidden until the issue is resolved.