A claim of type 'http://schemas.xmlsoap.org/ws/2005/05/identity/claims/nameidentifier' or 'http://schemas.microsoft.com/accesscontrolservice/2010/07/claims/identityprovider' was not present on the pro

Try setting (in global.cs):

AntiForgeryConfig.UniqueClaimTypeIdentifier = ClaimTypes.NameIdentifier;

I think it's important to note why this works: This tells the AntiForgery class to use the NameIdentifier (which is the user id string found by GetUserId).