[Feature] Facebook OAuth login

[fregataa]

Summary

Implement Facebook Login for user authentication.

Prerequisites

• [Feature] OAuth infrastructure setup #20 OAuth infrastructure setup

Scope

Setup

• Create Meta for Developers application
• Configure Facebook Login product
• Set Valid OAuth Redirect URIs
• Request email permission
• Complete app review (for public access)

Backend

• Add Facebook OAuth config (app ID, secret)
• Implement Facebook OAuth callback handler
• Exchange authorization code for access token
• Fetch user info from Graph API

Frontend

• Add "Continue with Facebook" button (with Meta brand guidelines)
• Handle Facebook OAuth redirect

Environment Variables

FACEBOOK_APP_ID=
FACEBOOK_APP_SECRET=
FACEBOOK_REDIRECT_URI=

Notes

• Facebook requires app review for email permission in production
• Consider privacy policy requirements

Acceptance Criteria

• Users can sign up/login with Facebook account
• Facebook account linked to user profile
• Follows Meta brand guidelines for login button

References

• Facebook Login Documentation