The authentication engine parses the protect string into one or more provider requests, and sends {HEAD ~ the requests} to {TAIL ~ the authentication host} 
The authentication engine parses the protect string into one or more provider requests , and sends { HEAD ~ the requests } to { TAIL ~ the authentication host }
OTH OTH OTH 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 TAIL