HSTS (Strict-Transport-Security) Header Generator & Preload Validator

# ====================================================================
# Nginx Configuration: Strict-Transport-Security (HSTS)
# Server Block: https://example.com
# ====================================================================
server {
    listen 443 ssl http2;
    listen [::]:443 ssl http2;
    server_name example.com *.example.com;

    # SSL Certificate Paths
    ssl_certificate /etc/letsencrypt/live/example.com/fullchain.pem;
    ssl_certificate_key /etc/letsencrypt/live/example.com/privkey.pem;

    # HSTS Security Header
    # Note: 'always' ensures the header is sent even on 4xx/5xx error responses
    add_header Strict-Transport-Security "max-age=63072000; includeSubDomains; preload" always;

    # Recommended Complementary Security Headers
    add_header X-Content-Type-Options "nosniff" always;
    add_header X-Frame-Options "DENY" always;
    add_header Referrer-Policy "strict-origin-when-cross-origin" always;

    location / {
        proxy_pass http://127.0.0.1:3000;
        proxy_set_header Host $host;
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header X-Forwarded-Proto https;
    }
}

# Redirect HTTP (Port 80) to HTTPS (Port 443)
# RFC 6797 §7.2: DO NOT send Strict-Transport-Security over insecure HTTP!
server {
    listen 80;
    listen [::]:80;
    server_name example.com *.example.com;
    return 301 https://$host$request_uri;
}