.net – 如何获取客户端DotNetOpenAuth.OAuth2返回的错误消息？

context.SetError("Autorization Error","The username or password is incorrect!");
context.Rejected();

但是在客户端，我只得到协议错误(错误400)。你可以帮助我如何在授权服务器上得到服务器端的错误信息？

授权服务器的完整应用配置：

using Constants;
using Microsoft.Owin;
using Microsoft.Owin.Security;
using Microsoft.Owin.Security.Cookies;
using Microsoft.Owin.Security.Infrastructure;
using Microsoft.Owin.Security.OAuth;
using Owin;
using System;
using System.Collections.Concurrent;
using System.Linq;
using System.Security.Claims;
using System.Security.Principal;
using System.Threading.Tasks;
using AuthorizationServer.Entities;
using AuthorizationServer.Entities.Infrastructure.Abstract;
using AuthorizationServer.Entities.Infrastructure.Concrete;

namespace AuthorizationServer
{
    public partial class Startup
    {
        private IEmployeeRepository Repository;  
        public void ConfigureAuth(IAppBuilder app)
        {
            //instanciate the repository
            Repository = new EmployeeRepository();

            // Enable Application Sign In Cookie
            app.UseCookieAuthentication(new CookieAuthenticationOptions
            {
                AuthenticationType = "Application",AuthenticationMode = AuthenticationMode.Passive,LoginPath = new PathString(Paths.LoginPath),LogoutPath = new PathString(Paths.LogoutPath),});

            // Enable External Sign In Cookie
            app.SetDefaultSignInAsAuthenticationType("External");
            app.UseCookieAuthentication(new CookieAuthenticationOptions
            {
                AuthenticationType = "External",CookieName = CookieAuthenticationDefaults.CookiePrefix + "External",ExpireTimeSpan = TimeSpan.FromMinutes(5),});

            // Enable google authentication
            app.UseGoogleAuthentication();

            // Setup Authorization Server
            app.USEOAuthAuthorizationServer(new OAuthAuthorizationServerOptions
            {
                AuthorizeEndpointPath = new PathString(Paths.AuthorizePath),TokenEndpointPath = new PathString(Paths.TokenPath),ApplicationCanDisplayErrors = true,#if DEBUG
                AllowInsecureHttp = true,#endif
                // Authorization server provider which controls the lifecycle of Authorization Server
                Provider = new OAuthAuthorizationServerProvider
                {
                    OnValidateClientRedirectUri = ValidateClientRedirectUri,OnValidateClientAuthentication = ValidateClientAuthentication,OnGrantResourceOwnerCredentials = GrantResourceOwnerCredentials,OnGrantClientCredentials = GrantClientCredetails
                },// Authorization code provider which creates and receives authorization code
                AuthorizationCodeProvider = new AuthenticationTokenProvider
                {
                    OnCreate = CreateAuthenticationCode,OnReceive = ReceiveAuthenticationCode,},// Refresh token provider which creates and receives referesh token
                RefreshTokenProvider = new AuthenticationTokenProvider
                {
                    OnCreate = CreateRefreshToken,OnReceive = ReceiveRefreshToken,}
            });

            // indicate our intent to use bearer authentication
            app.USEOAuthBearerAuthentication(new OAuthBearerAuthenticationOptions
            {
                AuthenticationType = "Bearer",AuthenticationMode = Microsoft.Owin.Security.AuthenticationMode.Active
            });
        }

        private Task ValidateClientRedirectUri(OAuthValidateClientRedirectUriContext context)
        {
            if (context.ClientId == Clients.Client1.Id)
            {
                context.Validated(Clients.Client1.RedirectUrl);
            }
            else if (context.ClientId == Clients.Client2.Id)
            {
                context.Validated(Clients.Client2.RedirectUrl);
            }
            return Task.FromResult(0);
        }

        private Task ValidateClientAuthentication(OAuthValidateClientAuthenticationContext context)
        {

            string clientname;
            string clientpassword;


            if (context.TryGetBasicCredentials(out clientname,out clientpassword) ||
                context.TryGetFormCredentials(out clientname,out clientpassword))
            {
                employee Employee = Repository.GetEmployee(clientname,clientpassword);

                if (Employee != null)
                {
                    context.Validated();
                }
                else
                {
                    context.SetError("Autorization Error","The username or password is incorrect!");
                    context.Rejected();
                }
            }
            return Task.FromResult(0);
        }

        private Task GrantResourceOwnerCredentials(OAuthGrantResourceOwnerCredentialsContext context)
        {
            var identity = new ClaimsIdentity(new GenericIdentity(context.UserName,OAuthDefaults.AuthenticationType),context.Scope.Select(x => new Claim("urn:oauth:scope",x)));

            context.Validated(identity);

            return Task.FromResult(0);
        }

        private Task GrantClientCredetails(OAuthGrantClientCredentialsContext context)
        {
            var identity = new ClaimsIdentity(new GenericIdentity(context.ClientId,x)));

            context.Validated(identity);

            return Task.FromResult(0);
        }


        private readonly ConcurrentDictionary<string,string> _authenticationCodes =
            new ConcurrentDictionary<string,string>(StringComparer.Ordinal);

        private void CreateAuthenticationCode(AuthenticationTokenCreateContext context)
        {
            context.SetToken(Guid.NewGuid().ToString("n") + Guid.NewGuid().ToString("n"));
            _authenticationCodes[context.Token] = context.SerializeTicket();
        }

        private void ReceiveAuthenticationCode(AuthenticationTokenReceiveContext context)
        {
            string value;
            if (_authenticationCodes.TryRemove(context.Token,out value))
            {
                context.DeserializeTicket(value);
            }
        }

        private void CreateRefreshToken(AuthenticationTokenCreateContext context)
        {
            context.SetToken(context.SerializeTicket());
        }

        private void ReceiveRefreshToken(AuthenticationTokenReceiveContext context)
        {
            context.DeserializeTicket(context.Token);
        }
    }
}