bereq.http.{NAME}
STRING, can be read, set and unset.
Request headers sent to the backend.
Before Fastly invokes vcl_miss or vcl_pass, we copy the contents of req.http.* into a new set of headers called bereq.http. This header list can then be modified without affecting the original request received from the client.
The bereq.http.* headers are also available in vcl_fetch, after the fetch to the backend has been made, but modifying their values in vcl_fetch has no effect.
