nginx's X-Forwarded-For is $proxy_add_x_forwarded_for, which only appends
to whatever the client sends — a forged leftmost hop passed straight
through, letting an attacker rotate spoofed values to dodge the 5s login
cooldown. X-Real-IP is set by nginx to $remote_addr on every proxied
location and can't be forged by the client, so key on that instead.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
