Configuring a Robust Content Security Policy (CSP) Header in Nginx

server {
    listen 80;
    server_name example.com www.example.com;

    # Redirect HTTP to HTTPS (recommended for production)
    return 301 https://$host$request_uri;
}

server {
    listen 443 ssl;
    server_name example.com www.example.com;

    ssl_certificate /etc/nginx/ssl/example.com.crt;
    ssl_certificate_key /etc/nginx/ssl/example.com.key;

    # Content Security Policy (CSP) Header
    # Restricts sources for various content types
    add_header Content-Security-Policy "
        default-src 'self' https://trusted.cdn.com;
        script-src 'self' 'unsafe-inline' 'unsafe-eval' https://ajax.googleapis.com;
        style-src 'self' 'unsafe-inline' https://fonts.googleapis.com;
        img-src 'self' data: https://img.example.com;
        font-src 'self' https://fonts.gstatic.com;
        connect-src 'self' https://api.example.com;
        frame-src 'self' https://www.youtube.com;
        object-src 'none';
        base-uri 'self';
        form-action 'self';
        frame-ancestors 'self';
        upgrade-insecure-requests;
        block-all-mixed-content;
        report-uri https://csp-reporting.example.com/report;
    " always;

    # Other security headers (for completeness, but focus is CSP)
    add_header X-Frame-Options "DENY" always;
    add_header X-Content-Type-Options "nosniff" always;
    add_header X-XSS-Protection "1; mode=block" always;
    add_header Referrer-Policy "no-referrer-when-downgrade" always;

    location / {
        proxy_pass http://localhost: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 $scheme;
    }
}