Option Name:httpd_accel_surrogate_id
Replaces:
Requires:
Default Value:visible_hostname is used if no specific ID is set.
Suggested Config:

	Surrogates (http://www.esi.org/architecture_spec_1.0.html)
	need an identification token to allow control targeting. Because
	a farm of surrogates may all perform the same tasks, they may share
	an identification token.

	When the surrogate is a reverse-proxy, this ID is also
	used as cdn-id for CDN-Loop detection (RFC 8586).