Show special message for GitHub 403 with option to jump to auth tokens

Cmdline/Action/Install.cs

@@ -244,6 +244,12 @@ public int RunCommand(CKAN.KSP ksp, object raw_options)
                 user.RaiseMessage(kraken.ToString());
                 return Exit.ERROR;
             }
+            catch (DownloadThrottledKraken kraken)
+            {
+                user.RaiseMessage(kraken.ToString());
+                user.RaiseMessage($"Try the authtoken command. See {kraken.infoUrl} for details.");
+                return Exit.ERROR;
+            }
             catch (DownloadErrorsKraken)
             {
                 user.RaiseMessage("One or more files failed to download, stopped.");

ConsoleUI/InstallScreen.cs

@@ -96,6 +96,13 @@ public override void Run(Action process = null)
                         RaiseError(ex.ToString());
                     } catch (ModuleDownloadErrorsKraken ex) {
                         RaiseError(ex.ToString());
+                    } catch (DownloadThrottledKraken ex) {
+                        if (RaiseYesNoDialog($"{ex.ToString()}\n\nEdit authentication tokens now?")) {
+                            if (ex.infoUrl != null) {
+                                ModInfoScreen.LaunchURL(ex.infoUrl);
+                            }
+                            LaunchSubScreen(new AuthTokenScreen());
+                        }
                     } catch (MissingCertificateKraken ex) {
                         RaiseError(ex.ToString());
                     } catch (InconsistentKraken ex) {

Core/Net/Net.cs

@@ -23,6 +23,14 @@ public class Net
         private static readonly ILog Log = LogManager.GetLogger(typeof (Net));
         private static readonly TxFileManager FileTransaction = new TxFileManager();
 
+        public static readonly Dictionary<string, Uri> ThrottledHosts = new Dictionary<string, Uri>()
+        {
+            {
+                "api.github.com",
+                new Uri("https://github.com/KSP-CKAN/CKAN/wiki/Adding-a-GitHub-API-authtoken")
+            }
+        };
+
         /// <summary>
         ///     Downloads the specified url, and stores it in the filename given.
         ///     If no filename is supplied, a temporary file will be generated.

Core/Net/NetAsyncDownloader.cs

@@ -301,10 +301,24 @@ public void DownloadAndWait(ICollection<Net.DownloadTarget> urls)
                 {
                     // Check if it's a certificate error. If so, report that instead,
                     // as this is common (and user-fixable) under Linux.
-                    if (downloads[i].error is WebException
-                        && certificatePattern.IsMatch(downloads[i].error.Message))
+                    if (downloads[i].error is WebException)
                     {
-                        throw new MissingCertificateKraken();
+                        WebException wex = downloads[i].error as WebException;
+                        if (certificatePattern.IsMatch(wex.Message))
+                        {
+                            throw new MissingCertificateKraken();
+                        }
+                        else switch ((wex.Response as HttpWebResponse)?.StatusCode)
+                        {
+                            // Handle HTTP 403 used for throttling
+                            case HttpStatusCode.Forbidden:
+                                Uri infoUrl;
+                                if (Net.ThrottledHosts.TryGetValue(downloads[i].url.Host, out infoUrl))
+                                {
+                                    throw new DownloadThrottledKraken(downloads[i].url, infoUrl);
+                                }
+                                break;
+                        }
                     }
                     // Otherwise just note the error and which download it came from,
                     // then throw them all at once later.

Core/Types/Kraken.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Net;
 using System.Text;
 using System.Collections.Generic;
 
@@ -380,6 +381,23 @@ public override string ToString()
         }
     }
 
+    public class DownloadThrottledKraken : Kraken
+    {
+        public readonly Uri throttledUrl;
+        public readonly Uri infoUrl;
+
+        public DownloadThrottledKraken(Uri url, Uri info) : base()
+        {
+            throttledUrl = url;
+            infoUrl      = info;
+        }
+
+        public override string ToString()
+        {
+            return $"Download from {throttledUrl.Host} was throttled.\r\nConsider adding an authentication token to increase the throtting limit.";
+        }
+    }
+
     public class RegistryInUseKraken : Kraken
     {
         public readonly string lockfilePath;

GUI/MainInstall.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Diagnostics;
 using System.Collections.Generic;
 using System.ComponentModel;
 using System.Linq;
@@ -194,6 +195,28 @@ private void InstallMods(object sender, DoWorkEventArgs e) // this probably need
                     GUI.user.RaiseMessage(kraken.ToString());
                     return;
                 }
+                catch (DownloadThrottledKraken kraken)
+                {
+                    string msg = kraken.ToString();
+                    GUI.user.RaiseMessage(msg);
+                    if (YesNoDialog($"{msg}\r\n\r\nOpen settings now?"))
+                    {
+                        // Launch the URL describing this host's throttling practices, if any
+                        if (kraken.infoUrl != null)
+                        {
+                            Process.Start(new ProcessStartInfo()
+                            {
+                                UseShellExecute = true,
+                                FileName        = kraken.infoUrl.ToString()
+                            });
+                        }
+                        // Now pretend they clicked the menu option for the settings
+                        Enabled = false;
+                        settingsDialog.ShowDialog();
+                        Enabled = true;
+                    }
+                    return;
+                }
                 catch (ModuleDownloadErrorsKraken kraken)
                 {
                     GUI.user.RaiseMessage(kraken.ToString());