public class OAuth2Issuer : IAuthorizationServer
    {
        private readonly IssuerConfiguration _configuration;

        public OAuth2Issuer(IssuerConfiguration configuration)
        {
            if (configuration == null) throw new ArgumentNullException("configuration");
            _configuration = configuration;
        }

        public RSACryptoServiceProvider AccessTokenSigningKey
        {
            get
            {
                return (RSACryptoServiceProvider)_configuration.SigningCertificate.PrivateKey;
            }
        }

        public DotNetOpenAuth.Messaging.Bindings.ICryptoKeyStore CryptoKeyStore
        {
            get { throw new NotImplementedException(); }
        }

        public TimeSpan GetAccessTokenLifetime(DotNetOpenAuth.OAuth2.Messages.IAccessTokenRequest accessTokenRequestMessage)
        {
            return _configuration.TokenLifetime;
        }

        public IClientDescription GetClient(string clientIdentifier)
        {
            const string secretPassword = "test1243";
            return new ClientDescription(secretPassword, new Uri("http://localhost/"), ClientType.Confidential);
        }

        public RSACryptoServiceProvider GetResourceServerEncryptionKey(DotNetOpenAuth.OAuth2.Messages.IAccessTokenRequest accessTokenRequestMessage)
        {
            return (RSACryptoServiceProvider)_configuration.EncryptionCertificate.PublicKey.Key;

        }

        public bool IsAuthorizationValid(DotNetOpenAuth.OAuth2.ChannelElements.IAuthorizationDescription authorization)
        {
            
            //claims added to the token
            authorization.Scope.Add("adminstrator");
            authorization.Scope.Add("poweruser");
            
            return true;
        }

        public bool IsResourceOwnerCredentialValid(string userName, string password)
        {
            return true;
        }

        public DotNetOpenAuth.Messaging.Bindings.INonceStore VerificationCodeNonceStore
        {
            get
            {
                throw new NotImplementedException();
            }
        }
    }

 public class OAuth2Handler : DelegatingHandler
    {
        private readonly ResourceServerConfiguration _configuration;

        public OAuth2Handler(ResourceServerConfiguration configuration)
        {
            if (configuration == null) throw new ArgumentNullException("configuration");
            _configuration = configuration;
        }

        protected override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
        {
            HttpContextBase httpContext;
            string userName;
            HashSet<string> scope;

            if (!request.TryGetHttpContext(out httpContext))
                throw new InvalidOperationException("HttpContext must not be null.");

            var resourceServer = new ResourceServer(new StandardAccessTokenAnalyzer(
                                                        (RSACryptoServiceProvider)_configuration.IssuerSigningCertificate.PublicKey.Key,
                                                        (RSACryptoServiceProvider)_configuration.EncryptionVerificationCertificate.PrivateKey));

            var error = resourceServer.VerifyAccess(httpContext.Request, out userName, out scope);

            if (error != null)
                return Task<HttpResponseMessage>.Factory.StartNew(error.ToHttpResponseMessage);
            
            var identity = new ClaimsIdentity(scope.Select(s => new Claim(s, s)));
            if (!string.IsNullOrEmpty(userName))
                identity.Claims.Add(new Claim(ClaimTypes.Name, userName));
            
            httpContext.User = ClaimsPrincipal.CreateFromIdentity(identity);
            Thread.CurrentPrincipal = httpContext.User;

            return base.SendAsync(request, cancellationToken);
        }

    }