protected override async Task <AuthenticateResult> HandleAuthenticateAsync()
        {
            // skip authentication if endpoint has [AllowAnonymous] attribute
            var endpoint = Context.GetEndpoint();

            if (endpoint?.Metadata?.GetMetadata <IAllowAnonymous>() != null)
            {
                return(AuthenticateResult.NoResult());
            }

            if (!Request.Headers.ContainsKey("Authorization"))
            {
                return(AuthenticateResult.Fail("Missing Authorization Header"));
            }
            var  authHeader      = AuthenticationHeaderValue.Parse(Request.Headers["Authorization"]);
            var  credentialBytes = Convert.FromBase64String(authHeader.Parameter);
            var  credentials     = Encoding.UTF8.GetString(credentialBytes).Split(new[] { ':' }, 2);
            var  username        = credentials[0];
            var  password        = credentials[1];
            User user            = await db.AuthAsync(username, password);

            if (user == null)
            {
                return(AuthenticateResult.Fail("Invalid Username or Password"));
            }

            var claims = new[] {
                new Claim(ClaimTypes.NameIdentifier, user.ID.ToString()),
                new Claim(ClaimTypes.Name, user.Login),
            };
            var identity  = new ClaimsIdentity(claims, Scheme.Name);
            var principal = new ClaimsPrincipal(identity);
            var ticket    = new AuthenticationTicket(principal, Scheme.Name);

            return(AuthenticateResult.Success(ticket));
        }