async Task <JwtToken> CreateTokenAsync(TokenRequestArgs args)
        {
            //sign and return access token along with refresh token
            var settings = new JwtTokenSettings
            {
                SigningKey = _tenant.SigningKey,
                Issuer     = _tenant.HostName,
                Audience   = _tenant.TenantName
            };
            var provider = new JwtTokenProvider(settings);
            var token    = await provider.SignAsync(args.username, null);

            token.refresh_token = args.refresh_token;
            return(token);
        }