AuthenticationExceptionHandlerMiddleware.cs

namespace SampleApi.Middleware
{
    using System;
    using System.Net;
    using System.Threading.Tasks;
    using Microsoft.AspNet.Builder;
    using Microsoft.AspNet.Http;
    using Microsoft.Extensions.Logging;

    public class AuthenticationExceptionHandlerMiddleware
    {
        public const string SuccessMarkerKey = "auth:success";

        private readonly RequestDelegate next;
        private readonly ILogger<AuthenticationExceptionHandlerMiddleware> logger;

        public AuthenticationExceptionHandlerMiddleware(
            RequestDelegate next,
            ILogger<AuthenticationExceptionHandlerMiddleware> logger)
        {
            if (next == null)
            {
                throw new ArgumentNullException(nameof(next));
            }

            if (logger == null)
            {
                throw new ArgumentNullException(nameof(logger));
            }

            this.next = next;
            this.logger = logger;
        }

        public async Task Invoke(HttpContext context)
        {
            // Set success marker to false
            context.Items[SuccessMarkerKey] = false;

            try
            {
                // Run rest of pipeline
                await this.next.Invoke(context);
            }
            catch (Exception e)
            {
                // Rethrow exception if authentication succeeded or the response has already started (can't help now)
                var authenticationSucceeded = context.Items[SuccessMarkerKey] as bool? ?? false;
                if (authenticationSucceeded || context.Response.HasStarted)
                {
                    throw;
                }

                // Authentication failed, return 401
                this.logger.LogError("Authentication failed with exception", e);
                context.Response.Headers.Clear();
                context.Response.StatusCode = (int)HttpStatusCode.Unauthorized;
            }
        }
    }
}