The present invention provides {HEAD ~ a highly scalable, flexible, and extensible mechanism} for authenticating {TAIL ~ a request} from a client 
for authenticating
The present invention provides { HEAD ~ a highly scalable , flexible , and extensible mechanism } for authenticating { TAIL ~ a request } from a client
OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH