The X-Forwarded-Host HTTP request header is required to forward the original Host HTTP request header value to the origin server.
When the user sends requests to https://abc.pfc.net/ , the request forwarded by F5 to the backend server
must contain the X-Forwarded-Host header with the value of the source of the request (which is https://abc.pfc.net/ in this example)
The backend server should be able to know what the host/FQDN from which the request came from so it will return to the client the same URL.