When HTTP header logging is enabled on a URL Filtering profile in Palo Alto Networks firewalls, the attribute-value that can be logged includes:
X-Forwarded-For (A): This HTTP header is commonly used to identify the originating IP address of a client connecting to a web server through an HTTP proxy or load balancer. Logging this header allows administrators to track the source IP addresses of clients accessing resources through proxies, providing better visibility into user activity.
References:
* Palo Alto Networks, URL Filtering Profiles Documentation.
* HTTP Header Field Definitions (RFC 7239).