Refactor timestamp provider handling and UI updates

Refactored timestamp provider logic for Trusted Signing and
regular signing, ensuring clearer separation of behavior.
Fixed timestamp URL for Trusted Signing and made it read-only.
Improved ComboBox population to show only enabled servers,
sorted by priority. Enhanced error handling with fallback
logic for endpoint selection and user notifications.

Updated UI elements to dynamically reflect signing type,
including editable timestamp URL for "Custom Provider."
Improved tooltips, logging, and user experience. Removed
redundant code and clarified comments for better
maintainability.

Author: michaelmsonne

src/SignToolGUI/Forms/MainForm.cs

@@ -416,7 +416,7 @@ private void PopulateComboBox()
 
             if (radioButtonTrustedSigning.Checked)
             {
-                // Switch to Trusted Signing servers - but only if we don't already have a loaded configuration
+                // For Trusted Signing: Use endpoint servers, but timestamp is always fixed
                 var currentServers = _timestampManager.GetServers();
                 var hasLoadedConfig = currentServers.Any(s => s.Url.Contains("codesigning.azure.net"));
 
@@ -434,12 +434,15 @@ private void PopulateComboBox()
 
                 groupBoxTimestamp.Text = @"Trusted Signing Endpoint";
                 labelTimestampProvider.Text = @"Endpoint region:";
+                labelTimeStampServer.Text = @"Timestamp URL:";
+
+                // For Trusted Signing, timestamp URL is always fixed
                 txtTimestampProviderURL.Text = @"http://timestamp.acs.microsoft.com";
-                labelTimeStampServer.Text = @"Endpoint URL:";
+                txtTimestampProviderURL.ReadOnly = true;
             }
             else
             {
-                // Switch to default timestamp servers - but only if we don't already have a loaded configuration
+                // For PFX and Certificate Store: Use timestamp servers from configuration
                 var currentServers = _timestampManager.GetServers();
                 var hasLoadedConfig = currentServers.Any(s => s.Url.Contains("timestamp.sectigo.com") ||
                                                               s.Url.Contains("timestamp.digicert.com"));
@@ -451,7 +454,8 @@ private void PopulateComboBox()
 
                 var servers = _timestampManager.GetServers();
 
-                foreach (var server in servers)
+                // Only add enabled servers to the dropdown for regular timestamp servers
+                foreach (var server in servers.Where(s => s.IsEnabled).OrderBy(s => s.Priority))
                 {
                     comboBoxTimestampProviders.Items.Add(new TimestampProvider(server.DisplayName, server.Url));
                 }
@@ -461,8 +465,11 @@ private void PopulateComboBox()
 
                 groupBoxTimestamp.Text = @"Timestamp";
                 labelTimestampProvider.Text = @"Provider:";
-                txtTimestampProviderURL.Text = "";
                 labelTimeStampServer.Text = @"Timestamp URL:";
+
+                // For regular timestamp servers, make URL editable when "Custom Provider" is selected
+                txtTimestampProviderURL.ReadOnly = false;
+                txtTimestampProviderURL.Text = "";
             }
 
             // Restore the previous selected index and item if they exist and are valid
@@ -602,10 +609,6 @@ private void RadioButtonSelectCertificateLocation_CheckedChanged(object sender,
                 textBoxSignToolPath.Enabled = false;
                 buttonBrowseSignTool.Enabled = false;
 
-                // Set the timestamp group box text and label text
-                groupBoxTimestamp.Text = @"Trusted Signing Endpoint";
-                labelTimeStampServer.Text = @"Endpoint URL:";
-
                 // Set the tooltip for the timestamp checkbox
                 toolTip.SetToolTip(checkBoxTimestamp, "Trusted Signing requires a timestamp. This option is disabled for Trusted Signing.");
             }
@@ -631,10 +634,6 @@ private void RadioButtonSelectCertificateLocation_CheckedChanged(object sender,
                 textBoxSignToolPath.Enabled = true;
                 buttonBrowseSignTool.Enabled = true;
 
-                // Set the timestamp group box text and label text
-                groupBoxTimestamp.Text = @"Timestamp URL:";
-                labelTimeStampServer.Text = @"Timestamp";
-
                 // Reset the tooltip for the timestamp checkbox
                 toolTip.SetToolTip(checkBoxTimestamp, "Check this box to timestamp the signed file(s).");
             }
@@ -826,23 +825,36 @@ private void comboBoxTimestampProviders_SelectedIndexChanged(object sender, Even
             TimestampProvider selectedProvider = comboBox.SelectedItem as TimestampProvider;
             if (selectedProvider == null) return;
 
-            // Update the timestamp provider URL text box with the selected provider's URL.
-            txtTimestampProviderURL.Text = selectedProvider.Url;
-
-            // Get the selected index from the timestamp providers combo box.
-            var index = comboBoxTimestampProviders.SelectedIndex;
-
-            // If the selected index is not 5, make the timestamp provider URL text box read-only.
-            if (index != 5)
+            if (radioButtonTrustedSigning.Checked)
             {
-                // Make the timestamp provider URL text box read-only.
+                // For Trusted Signing: The selected item is an endpoint, but timestamp URL is always fixed
+                // The selectedProvider.Url is the endpoint URL, not the timestamp URL
+
+                // Keep the timestamp URL fixed for Trusted Signing
+                txtTimestampProviderURL.Text = @"http://timestamp.acs.microsoft.com";
                 txtTimestampProviderURL.ReadOnly = true;
+
+                // Store the selected endpoint for use during signing (this should be handled in the signing logic)
+                // The actual endpoint selection happens in the signing process
             }
             else
             {
-                // If the selected index is 5, clear the timestamp provider URL text box and make it editable.
-                txtTimestampProviderURL.Clear();
-                txtTimestampProviderURL.ReadOnly = false;
+                // For regular timestamp servers: Update the URL based on selection
+
+                // Check if "Custom Provider" is selected
+                if (selectedProvider.DisplayName == "Custom Provider")
+                {
+                    // If Custom Provider is selected, clear the URL and make it editable
+                    txtTimestampProviderURL.Clear();
+                    txtTimestampProviderURL.ReadOnly = false;
+                    txtTimestampProviderURL.Focus(); // Set focus to the text box for user input
+                }
+                else
+                {
+                    // Update the timestamp provider URL text box with the selected provider's URL
+                    txtTimestampProviderURL.Text = selectedProvider.Url;
+                    txtTimestampProviderURL.ReadOnly = true;
+                }
             }
         }
 
@@ -1563,12 +1575,36 @@ private async Task SignWithTrustedSigningAsync()
             // Get the values from the form's controls for the SignerTrustedSigning class
             var signToolExe = textBoxSignToolPath.Text;
             var timeStampServer = "http://timestamp.acs.microsoft.com"; // Fixed timestamp server for Trusted Signing
-            var endpointServer = txtTimestampProviderURL.Text; // This is actually the regional endpoint
+
+            // Get the selected endpoint from the ComboBox
+            string endpointServer = "";
+            if (comboBoxTimestampProviders.SelectedItem is TimestampProvider selectedProvider)
+            {
+                endpointServer = selectedProvider.Url;
+            }
+            else
+            {
+                // Fallback to first enabled server if nothing is selected
+                var enabledServers = _timestampManager.GetEnabledServers();
+                if (enabledServers.Count > 0)
+                {
+                    endpointServer = enabledServers.First().Url;
+                }
+                else
+                {
+                    MessageBox.Show("No enabled Trusted Signing endpoints available.", "Configuration Error", MessageBoxButtons.OK, MessageBoxIcon.Error);
+                    return;
+                }
+            }
+
             var dlibPath = @".\Tools\Azure.CodeSigning.Dlib.dll";
             var codeSigningAccountName = textBoxCodeSigningAccountName.Text;
             var certificateProfileName = textBoxCertificateProfileName.Text;
             var correlationIdData = textBoxCorrelationId.Text;
 
+            // Log which endpoint is being used
+            Message($"Using Trusted Signing endpoint: {endpointServer}", EventType.Information, 3025);
+
             // Disable the form's controls while signing the files
             ToggleDisabledForm(true);