X-forwarded Http irule

You can use an HTTP profile with the Insert X-Forwarded-For setting enabled instead of an iRule and save a little performance overhead. With respect to Hostname, Hostname is already available in the HTTP Host header. There is nothing you need to do no the BIG-IP system to have that passed to the back end server. With respect to Username, the assumption, is for BIG-IP to be aware of it, it must be passed in the payload somewhere already, perhaps in a cookie or the HTTP query string. If so, you don't need to do anything on BIG-IP to have it passed to the back end server.