Don't try to use explicit credentials with schemes that don't support it.

net/http/http_auth_handler_negotiate.cc

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "net/http/http_auth_handler_negotiate.h"
 
 #include "base/logging.h"
 #include "base/string_util.h"
 #include "base/stringprintf.h"
 #include "base/utf_string_conversions.h"
@@ skipping 164 matching lines @@
 }
 
 bool HttpAuthHandlerNegotiate::AllowsDefaultCredentials() {
   if (target_ == HttpAuth::AUTH_PROXY)
     return true;
   if (!url_security_manager_)
     return false;
   return url_security_manager_->CanUseDefaultCredentials(origin_);
 }
 
+bool HttpAuthHandlerNegotiate::AllowsExplicitCredentials() {
+  return auth_system_.AllowsExplicitCredentials();
+}
+
 // The Negotiate challenge header looks like:
 //   WWW-Authenticate: NEGOTIATE auth-data
 bool HttpAuthHandlerNegotiate::Init(HttpAuth::ChallengeTokenizer* challenge) {
 #if defined(OS_POSIX)
   if (!auth_system_.Init()) {
     VLOG(1) << "can't initialize GSSAPI library";
     return false;
   }
   // GSSAPI does not provide a way to enter username/password to
   // obtain a TGT. If the default credentials are not allowed for
@@ skipping 135 matching lines @@
 bool HttpAuthHandlerNegotiate::CanDelegate() const {
   // TODO(cbentzel): Should delegation be allowed on proxies?
   if (target_ == HttpAuth::AUTH_PROXY)
     return false;
   if (!url_security_manager_)
     return false;
   return url_security_manager_->CanDelegate(origin_);
 }
 
 }  // namespace net