When we get an authentication failure, we must consume the entire body
of the response. If we only read half of the body (on the assumption
that we can ignore the rest) then we will never complete the parsing of
the message. This means that we will never set the complete flag, and
our replay must actually tear down the connection and try again.
This is particularly problematic for stateful authentication mechanisms
(SPNEGO, NTLM) that require that we keep the connection alive.
Note that the prior code is only a problem when the 401 that we are
parsing is too large to be read in a single chunked read from the http
parser.
But now we will continue to invoke the http parser until we've got a
complete message in the authentication failed scenario. Note that we
need not do anything with the message, so when we get an authentication
failed, we'll stop adding data to our buffer, we'll simply loop in the
parser and let it advance its internal state.
