ASP.NET Web API 通过Authentication特性来实现身份认证

using System;
using System.Collections.Generic;
using System.Net.Http.Headers;
using System.Security.Principal;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
using System.Web.Http.Filters;
using System.Web.Http.Results;

namespace WebApi
{
    [AttributeUsage(AttributeTargets.Class | AttributeTargets.Method)]
    public class AuthenticateAttribute : FilterAttribute, IAuthenticationFilter
    {
        private static readonly Dictionary<string, string> UserAccounts;

        static AuthenticateAttribute()
        {
            UserAccounts = new Dictionary<string, string>(StringComparer.OrdinalIgnoreCase)
            {
                {"Foo", "Password"},
                {"Bar", "Password"},
                {"Baz", "Password"}
            };
        }

        public Task AuthenticateAsync(HttpAuthenticationContext context, CancellationToken cancellationToken)
        {
            IPrincipal user = null;
            var headerValue = context.Request.Headers.Authorization;
            if (null != headerValue && headerValue.Scheme == "Basic")
            {
                var credential = Encoding.Default.GetString(Convert.FromBase64String(headerValue.Parameter));
                var split = credential.Split(':');
                if (split.Length == 2)
                {
                    var userName = split[0];
                    string password;
                    if (UserAccounts.TryGetValue(userName, out password))
                    {
                        if (password == split[1])
                        {
                            var identity = new GenericIdentity(userName);
                            user = new GenericPrincipal(identity, new string[0]);
                        }
                    }
                }
            }
            context.Principal = user;
            return Task.FromResult<object>(null);
        }

        public Task ChallengeAsync(HttpAuthenticationChallengeContext context, CancellationToken cancellationToken)
        {
            var user = context.ActionContext.ControllerContext.RequestContext.Principal;
            if (null != user && user.Identity.IsAuthenticated) return Task.FromResult<object>(null);
            var parameter = $"realm={context.Request.RequestUri.DnsSafeHost}";
            var challenge = new AuthenticationHeaderValue("Basic", parameter);
            context.Result = new UnauthorizedResult(new[] {challenge}, context.Request);
            return Task.FromResult<object>(null);
        }
    }
}