ASP.NET Core - getting a message back from AuthenticationHandler

I have implemented a subclass of AuthenticationHandler. It returns AuthenticationResult.Fail("This is why you can't log in");

I would have expected this message to end up in the body, or at least in the HTTP status text, but instead I get a blank 401 response.

Is there any way to provide additional information for failed authentication attempts in ASP.NET core?

For changing the body or Http status, you could try Context.Response.

Here is a demo code:

using Microsoft.AspNetCore.Authentication;
using Microsoft.Extensions.Logging;
using Microsoft.Extensions.Options;
using System.Text.Encodings.Web;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Http;
namespace TestIdentity
{
    public class CustomAuthenticationHandler<TOptions> : AuthenticationHandler<TOptions> where TOptions : AuthenticationSchemeOptions, new()
    {
        public CustomAuthenticationHandler(IOptionsMonitor<TOptions> options
            , ILoggerFactory logger
            , UrlEncoder encoder, ISystemClock clock) : base(options, logger, encoder, clock)
        {

        }
        protected override async Task<AuthenticateResult> HandleAuthenticateAsync()
        {
            await Context.Response.WriteAsync("This is why you can't log in");
            return AuthenticateResult.Fail("This is why you can't log in");
        }
    }
}