An engineer needs to collect User-ID mappings from the company’s existing proxies.

Palo Alto firewalls can gather User-ID mappings from proxies via Syslog (Option B), parsing log messages with user-IP data, and XFF Headers (Option D), extracting user info from HTTP headers (X-Forwarded-For) if the proxy supports it.

Option A (Client Probing) queries clients, not proxies. Option C (Server Monitoring) targets servers like AD, not proxies. Documentation lists these methods for proxy integration.