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