The auth routes were registered under /admin/* but the IndieAuth
redirect_uri was configured as /auth/callback, causing 404 errors
when providers redirected back after authentication.
- Change auth blueprint url_prefix from "/admin" to "/auth"
- Update test expectations for new auth route paths
- Add ADR-022 documenting the architectural decision
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude <noreply@anthropic.com>
