STRING, can be read,
Available inall subroutines.
Request headers sent by the client.
IMPORTANT: Use of the data exposed by these variables could, in some cases, introduce ossification risk to the internet.
Request headers are also frequently used as variables to store strings for later use. Fastly VCL also offers local variables as an alternative for storing temporary values.
Due to Fastly's clustering, request headers set in a subroutine that runs on a fetch node will not be transferred back to the deliver node.