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

net/http/http_auth_gssapi_posix.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_gssapi_posix.h"
 
 #include <limits>
 #include <string>
 
 #include "base/base64.h"
@@ skipping 658 matching lines @@
 bool HttpAuthGSSAPI::Init() {
   if (!library_)
     return false;
   return library_->Init();
 }
 
 bool HttpAuthGSSAPI::NeedsIdentity() const {
   return decoded_server_auth_token_.empty();
 }
 
+bool HttpAuthGSSAPI::AllowsExplicitCredentials() const {
+  return false;
+}
+
 void HttpAuthGSSAPI::Delegate() {
   can_delegate_ = true;
 }
 
 HttpAuth::AuthorizationResult HttpAuthGSSAPI::ParseChallenge(
     HttpAuth::ChallengeTokenizer* tok) {
   // Verify the challenge's auth-scheme.
   if (!LowerCaseEqualsASCII(tok->scheme(), StringToLowerASCII(scheme_).c_str()))
     return HttpAuth::AUTHORIZATION_RESULT_INVALID;
 
@@ skipping 194 matching lines @@
   if (rv != OK) {
     LOG(ERROR) << "Problem initializing context. \n"
                << DisplayExtendedStatus(library_, major_status, minor_status)
                << '\n'
                << DescribeContext(library_, scoped_sec_context_.get());
   }
   return rv;
 }
 
 }  // namespace net