httpd_accel_uses_host_header
When this directive is enabled, Squid uses a request’s Host header when rewriting
accelerated/intercepted requests. When disabled, Squid uses either the
origin server’s IP address or the
httpd_accel_host value.
You should probably enable httpd_accel_uses_host_header when running Squid as an HTTP-intercepting proxy. If Squid is a surrogate (accelerator), you only need to enable this directive if the backend server is configured for virtual hosting.