A highly scalable, flexible, and extensible mechanism is provided for authenticating {HEAD ~ a request} from {TAIL ~ a client} 
from
A highly scalable , flexible , and extensible mechanism is provided for authenticating { HEAD ~ a request } from { TAIL ~ a client }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL