http {
    # ... other http configurations ...

    map $http_authorization $is_s3_auth {
        default 0;
        ~AWS4-HMAC-SHA256 1; # Check for AWS S3 v4 authorization
    }

    server {
        listen 80; # Or your desired port
        server_name yourdomain.com; # Or your domain

        location / {
            if ($request_method = PUT) {
                if ($is_s3_auth = 1) {
                    # PUT request with S3 authorization: proxy to s3_backend
                    proxy_pass http://s3_backend;
                    break; # Stop further processing in this location
                }
            }
            # All other requests (or PUT without S3 auth): proxy to default_backend
            proxy_pass http://default_backend;
        }

        # ... other locations ...
    }

    # ... other http configurations ...
}