SharePoint 2010 Client Object Model - Kerberos/Claims Authentication - sharepoint

Question

I'm trying to read a value from a list in a remote SharePoint site (different SP Web App). The web apps are set up with Claims Auth, and the client web app SP Managed account is configured with an SPN. I believe Kerberos and claims are set up correctly, but I am unable to reach the remote server, and the request causes an exception: "The remote server returned an error: (401) Unauthorized."
The exception occurs in the line ctx.ExecuteQuery(); but it does not catch the exception in the if (scope.HasException) instead, the exception is caught by the calling code (outside of the using{} block).
When I look at the traffic at the remote server using Wireshark, it doesn't look like the request is even getting to the server; it's almost as if the 401 occurs before the Kerberos ticket is exchanged for the claim.
Here's my code:
using (ClientContext ctx = new ClientContext(contextUrl))
{
CredentialCache cc = new CredentialCache();
cc.Add(new Uri(contextUrl), "Kerberos", CredentialCache.DefaultNetworkCredentials);
ctx.Credentials = cc;
ctx.AuthenticationMode = ClientAuthenticationMode.Default;
ExceptionHandlingScope scope = new ExceptionHandlingScope(ctx);
Web ctxWeb = ctx.Web;
List ctxList;
Microsoft.SharePoint.Client.ListItemCollection listItems;
using (scope.StartScope())
{
using (scope.StartTry())
{
ctxList = ctxWeb.Lists.GetByTitle("Reusable Content");
CamlQuery qry = new CamlQuery();
qry.ViewXml = string.Format(ViewQueryByField, "Title", "Text", SharedContentTitle);
listItems = ctxList.GetItems(qry);
ctx.Load(listItems, items => items.Include(
item => item["Title"],
item => item["ReusableHtml"],
item => item["ReusableText"]));
}
using (scope.StartCatch()) { }
using (scope.StartFinally()) { }
}
ctx.ExecuteQuery();
if (scope.HasException)
{
result = string.Format("Error retrieving content<!-- Error Message: {0} | {1} -->", scope.ErrorMessage, contextUrl);
}
if (listItems.Count == 1)
{
Microsoft.SharePoint.Client.ListItem contentItem = listItems[0];
if (SelectedType == SharedContentType.Html)
{
result = contentItem["ReusableHtml"].ToString();
}
else if (SelectedType == SharedContentType.Text)
{
result = contentItem["ReusableText"].ToString();
}
}
}
I realize the part with the CredentialCache shouldn't be necessary in claims, but every single example I can find is either running in a console app, or in a client side application of some kind; this code is running in the codebehind of a regular ASP.NET UserControl.
Edit: I should probably mention, the code above doesn't even work when the remote URL is the root site collection on the same web app as the calling code (which is in a site collection under /sites/)--in other words, even when the hostname is the same as the calling code.
Any suggestions of what to try next are greatly appreciated!
Mike

Answer 1

Is there a reason why you are not using the standard OM?
You already said this is running in a web part, which means it is in the context of application pool account. Unless you elevate permissions by switching users, it won't authenticate correctly. Maybe try that. But I would not use the client OM when you do have access to the API already.