We have previously used Windows Authentication together with an IClaimsTransformation to authenticate users for the CMS and Admin parts of our website.

This was done by simply using AddNegotiate after CMS and Authentication in our startup.cs ConfigureServices method.

After updating nugets from CMS 12.17.1 to 12.26.1 we now get an error indicating "Attempting to use an incomplete authentication context." from the NegotiateHandler.

According to the aspnetcore source code on github this only happens if _negotiateState.IsCompleted is not true, which comments say shouldn't happen.

Is there any change in the CMS versions between 17 and 26 (or related nugets) that might cause this, and if so, how can the error be corrected? The only thing that changes between our auth setup working and not working is the nuget version change.

The following code used to work, but doesn't now (the IClaimsTransformation class is never reached because of the error thrown):

services.AddCmsAspNetIdentity<ApplicationUser>()
                .AddCms()
                .AddAuthentication(options =>
                {
                    options.DefaultScheme = "Windows";
                    options.DefaultAuthenticateScheme = "Windows";
                    options.DefaultChallengeScheme = "Windows";
                })
                .AddNegotiate("Windows", options => { });
            services.TryAddEnumerable(ServiceDescriptor.Singleton<IClaimsTransformation, ADGroupToRolesTransformer>());
services.AddAuthorization(options =>
            {
                options.FallbackPolicy = options.DefaultPolicy;
            });

And here's a short stacktrace of the issue.

InvalidOperationException: Attempting to use an incomplete authentication context.
Microsoft.AspNetCore.Authentication.Negotiate.NegotiateHandler.HandleAuthenticateAsync()
Microsoft.AspNetCore.Authentication.AuthenticationHandler<TOptions>.AuthenticateAsync()
Microsoft.AspNetCore.Authentication.AuthenticationService.AuthenticateAsync(HttpContext context, string scheme)
Microsoft.AspNetCore.Authentication.AuthenticationMiddleware.Invoke(HttpContext context)
Microsoft.AspNetCore.Diagnostics.StatusCodePagesMiddleware.Invoke(HttpContext context)
Microsoft.AspNetCore.Diagnostics.ExceptionHandlerMiddleware.<Invoke>g__Awaited|6_0(ExceptionHandlerMiddleware middleware, HttpContext context, Task task)
Microsoft.AspNetCore.Diagnostics.ExceptionHandlerMiddleware.HandleException(HttpContext context, ExceptionDispatchInfo edi)
Microsoft.AspNetCore.Diagnostics.ExceptionHandlerMiddleware.<Invoke>g__Awaited|6_0(ExceptionHandlerMiddleware middleware, HttpContext context, Task task)
Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddleware.Invoke(HttpContext context)