Don't use IDENT_SRC_URL for HttpAuth challenges. IE hasn't supported it for years, and at worst ...

net/http/http_network_transaction.cc

Index: net/http/http_network_transaction.cc
===================================================================
--- net/http/http_network_transaction.cc	(revision 120359)
+++ net/http/http_network_transaction.cc	(working copy)
@@ -1290,9 +1290,14 @@
   if (!auth_controllers_[target].get())
     return ERR_UNEXPECTED_PROXY_AUTH;
 
+  int option_mask = 0;
+  if (!(request_->load_flags & LOAD_DO_NOT_SEND_AUTH_DATA))
+    option_mask |= HttpAuthController::CHALLENGE_OPTION_SEND_SERVER_AUTH;
+  if ((request_->load_flags & LOAD_ENABLE_EMBEDDED_IDENTITY))
+    option_mask |= HttpAuthController::CHALLENGE_OPTION_USE_EMBEDDED_AUTH;
+
   int rv = auth_controllers_[target]->HandleAuthChallenge(
-      headers, (request_->load_flags & LOAD_DO_NOT_SEND_AUTH_DATA) != 0, false,
-      net_log_);
+      headers, option_mask, net_log_);
   if (auth_controllers_[target]->HaveAuthHandler())
       pending_auth_target_ = target;