The Wikimedia Stewards were emailed by Zscaler (Ticket#2021122310004481 ), asking for help with their customers unable to edit Wikipedia because of soft-blocked Zscaler nodes.
Zscaler confirmed they add XFF to the requests. This means we can add them to the list of trusted hosts for XFF: IPs available at https://config.zscaler.com/zscaler.net/cenr. Patch incoming.