When cache expiration is set to sliding, the Cache-Control HTTP header will be renewed with each response. This expiration mode is identical to the IIS configuration option to add an expiration header to all output set relative to the current time.
If you explicitly set sliding expiration to off (false), that setting will be preserved and any attempts to enable sliding expiration will silently fail. This method does not directly map to an HTTP header. It is used by subsequent modules or worker requests to set origin-server cache policy.