Fix 401 Unauthorized Exception uploading file to SharePoint 2010

Question

I have a WCF service hosted in IIS on Domain 1. This service is accepting a request to upload a file, and then uploading the file to a SharePoint 2010 Server on Domain 2, using the client object model.

Everything works fine when I hardcode the username, password & domain using:

context.Credentials = new NetworkCredential(login, password, domain);

However, due to the compliance & security we cannot do this in our company. We need to use integrated security if possible. I have tried setting the credentials to both

context.Credentials = CredentialCache.DefaultCredentials;
context.Credentials = CredentialCache.DefaultNetworkCredentials;

But neither appear to work, we receive the error

System.Net.WebException: The remote server returned an error: (401) Unauthorized. at System.Net.HttpWebRequest.GetResponse() at Microsoft.SharePoint.Client.SPWebRequestExecutor.Execute() at Microsoft.SharePoint.Client.ClientContext.GetFormDigestInfoPrivate() at Microsoft.SharePoint.Client.ClientContext.EnsureFormDigest() at Microsoft.SharePoint.Client.ClientContext.ExecuteQuery()

Can someone provide any tips on how to fix this? Or tips that might lead us to the resolution, logs to check etc. I am not the developer of the SharePoint site, but can chase them down. I have gone through many questions/answers here and none seem to help us.

Answer 1

Set the authentication mode as shown below

context.AuthenticationMode = ClientAuthenticationMode.Default;

Also make sure the application pool account under which the service is hosted in IIS has proper access to SharePoint document library.

Answer 2

It won't work with default credentials because application pool identity is not there in normal context. If you check the result of System.Security.Principal.WindowsIdentity.GetCurrent() method, you'll see it returns IUSR instead.

If you want to execute code with app pool credentials, you need to elevate permissions using SPSecurity.RunWithElevatedPrivileges().