events {
    worker_connections 2048;
}

http {
    upstream flask_backend {
        server api:5001;
    }

    server {
        listen 443 ssl;
        server_name _;

        # Server certificate (HTTPS)
        ssl_certificate /etc/nginx/certs/server.crt;
        ssl_certificate_key /etc/nginx/certs/server.key;

        # Client certificate validation (optional during rollout)
        # optional_no_ca: accept cert but don't validate against CA
        # Flask validates fingerprint against database
        ssl_verify_client optional_no_ca;

        # Increase timeouts for long-polling agents
        proxy_connect_timeout 90s;
        proxy_send_timeout 90s;
        proxy_read_timeout 90s;

        # All routes
        location / {
            proxy_pass http://flask_backend;
            proxy_http_version 1.1;
            proxy_set_header Connection "";

            # Pass real client IP (not nginx IP)
            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 $scheme;
            proxy_set_header Host $host;

            # Pass client certificate fingerprint to Flask
            # SECURITY NOTE: $ssl_client_fingerprint outputs SHA1 (40 hex chars),
            # not SHA256. This is a known nginx limitation. SHA1 is acceptable for
            # certificate fingerprinting (not signing) in air-gapped environments
            # with short-lived certs and revocation support.
            # Format: "AB:CD:EF:..." (colon-separated hex, normalized in Flask)
            # Future SHA256: requires custom nginx module or migrate to IIS
            proxy_set_header X-Client-Cert-Fingerprint $ssl_client_fingerprint;
            proxy_set_header X-Client-Cert-S-DN $ssl_client_s_dn;
        }

        # Access log includes client cert status
        access_log /dev/stdout combined;
        error_log /dev/stderr warn;
    }
}