The remote server returned an error: (401) Unauthorized. Using CSOM in ASP.NET

Question

I'm tried to pull some SharePoint 2013 list data I created which works fine when running locally on my machine and when run locally one the server. I'm user the same credentials when running both locally and locally on the server. The issue is when I publish and navigate to my ASP.NET app on the server I get the "The remote server returned an error: (401) Unauthorized." Error...

I've looked at a bunch of the posts on stackoverflow and some other articles on the web

This points out that the context seems to be using IUSR: http://blogs.msdn.com/b/sridhara/archive/2014/02/06/sharepoint-2013-csom-call-from-web-part-fails-with-401-for-all-users.aspx

This one mentions to try setting the default network credentials: https://sharepoint.stackexchange.com/questions/10364/http-401-unauthorized-using-the-managed-client-object-model

I've tried using the fixes mentioned in the article as well as trying to force the context to use DefaultNetworkCredentials but no luck. I would like for the app to use the credentials of the logged in user and not the machine...

Here is the code I'm using:

        SP.ClientContext context = new SP.ClientContext("MySPDevInstance");
        context.Credentials = CredentialCache.DefaultNetworkCredentials;

        Entity entity = context.Web.GetEntity(collectionNamespace, collectionName);
        LobSystem lobSystem = entity.GetLobSystem();
        LobSystemInstanceCollection lobSystemInstanceCollection = lobSystem.GetLobSystemInstances();

        context.Load(lobSystemInstanceCollection);
        context.ExecuteQuery();

        LobSystemInstance lobSystemInstance = lobSystemInstanceCollection[0];
        FilterCollection filterCollection = entity.GetFilters(filter);

        filterCollection.SetFilterValue("LimitFilter", 0, 1000);

        EntityInstanceCollection items = entity.FindFiltered(filterCollection, filter, lobSystemInstance);

The server is running IIS 6.0

Any advice would be much appreciated!

Thank you

Answer 1

I presume your ASP.NET web site is using Windows Integrated (NTLM) authentication. A user authenticated this way cannot authenticate to a second location from the server side (the web server.) You are experiencing what is known as the "double-hop" (1) limitation of NTLM. You must use a dedicated account on the server side, or if you really do want to use the logged-in user's identity, you must use an authentication scheme that permits delegation, such as Kerberos.

If you really need the user's identity to access SharePoint data and you cannot change the authentication scheme, then the best way to do this is to use the JavaScript CSOM. This means the user is authenticating directly to the SharePoint server (a single hop, not double) and your ASP.NET site serves the page containing this script to the user.

(1) http://blogs.msdn.com/b/knowledgecast/archive/2007/01/31/the-double-hop-problem.aspx