AzureFunctions.Authentication.FrontEndAuthProvider.TryGetTenantForSubscription C# (CSharp) Method

        private bool TryGetTenantForSubscription(string subscriptionId, out string tenantId)
        {
            tenantId = string.Empty;
            var requestUri = string.Format(Constants.SubscriptionTemplate, Constants.CSMUrl, subscriptionId, Constants.CSMApiVersion);
            var request = WebRequest.CreateHttp(requestUri);
            using (var response = request.GetResponseWithoutExceptions())
            {
                if (response.StatusCode != HttpStatusCode.Unauthorized)
                {
                    System.Diagnostics.Trace.TraceError(string.Format("Expected status {0} != {1} GET {2}", HttpStatusCode.Unauthorized, response.StatusCode, requestUri));
                    return false;
                }

                var header = response.Headers["WWW-Authenticate"];
                if (header == null || string.IsNullOrEmpty(header))
                {
                    System.Diagnostics.Trace.TraceError(string.Format("Missing WWW-Authenticate response header GET {0}", requestUri));
                    return false;
                }

                // WWW-Authenicate: Bearer authorization_uri="https://login.windows.net/{tenantId}", error="invalid_token", error_description="The access token is missing or invalid."
                var index = header.IndexOf("authorization_uri=", StringComparison.OrdinalIgnoreCase);
                if (index == -1)
                {
                    System.Diagnostics.Trace.TraceError(string.Format("Invalid WWW-Authenticate response header {0} GET {1}", header, requestUri));
                    return false;
                }

                tenantId =
                    header.Substring(index).Split(new[] { '\"', '=' }, StringSplitOptions.RemoveEmptyEntries)
                    .Skip(1)
                    .Take(1)
                    .Select(s => new Uri(s).AbsolutePath.Trim('/'))
                    .First();
                return !string.IsNullOrEmpty(tenantId);
            }
        }