Zscaler This document defines a lightweight mechanism that allows explicit HTTP proxies to inform clients when their proxy configuration, such as a Proxy Auto-Configuration (PAC) file or Provisioning Domain (PvD) proxy configuration, is outdated. Clients signal to the proxy the configuration URL and the timestamp of when it was last fetched. In response, the proxy may indicate that a newer version of the configuration is available. This enables clients to refresh their configuration without relying on frequent polling or short expiration intervals. The mechanism is designed to be compatible with existing proxy deployment models and supports both PAC-based and PvD-based configurations.