Provide better tooltip when login fails

When the user provides a personal access token instead of their
password, the API responds with a 403. We should show a more helpful
error message here.

Fixes #14

Author: haacked

src/GitHub.App/ViewModels/LoginTabViewModel.cs

@@ -41,9 +41,17 @@ protected LoginTabViewModel(IRepositoryHosts repositoryHosts, IVisualStudioBrows
 
             Login.ThrownExceptions.Subscribe(ex =>
             {
-                if (!ex.IsCriticalException())
+                if (ex.IsCriticalException()) return;
+
+                log.Info(string.Format(CultureInfo.InvariantCulture, "Error logging into '{0}' as '{1}'", BaseUri,
+                    UsernameOrEmail), ex);
+                if (ex is ForbiddenException)
+                {
+                    ShowLogInFailedError = true;
+                    LoginFailedMessage = "Make sure to use your password and not a Personal Access token to log in.";
+                }
+                else
                 {
-                    log.Info(string.Format(CultureInfo.InvariantCulture, "Error logging into '{0}' as '{1}'", BaseUri, UsernameOrEmail), ex);
                     ShowConnectingToHostFailed = true;
                 }
             });

src/GitHub.Exports.Reactive/ViewModels/ILoginToHostViewModel.cs

@@ -59,6 +59,11 @@ public interface ILoginToHostViewModel
         /// </summary>
         bool ShowLogInFailedError { get; }
 
+        /// <summary>
+        /// The message to show if login failed.
+        /// </summary>
+        string LoginFailedMessage { get; }
+
         /// <summary>
         /// Gets a command which, when invoked, resets all properties 
         /// and validators.

src/UnitTests/GitHub.App/ViewModels/LoginToGitHubViewModelTests.cs

@@ -1,14 +1,39 @@
 using System;
+using System.Net;
+using System.Reactive.Linq;
+using GitHub.Authentication;
 using GitHub.Info;
 using GitHub.Models;
 using GitHub.Primitives;
 using GitHub.Services;
 using GitHub.ViewModels;
 using NSubstitute;
+using Octokit;
 using Xunit;
 
 public class LoginToGitHubViewModelTests
 {
+    public class TheLoginCommand : TestBaseClass
+    {
+        [Fact]
+        public void ShowsHelpfulTooltipWhenForbiddenResponseReceived()
+        {
+            var response = Substitute.For<IResponse>();
+            response.StatusCode.Returns(HttpStatusCode.Forbidden);
+            var repositoryHosts = Substitute.For<IRepositoryHosts>();
+            repositoryHosts.LogIn(HostAddress.GitHubDotComHostAddress, Args.String, Args.String)
+                .Returns(_ => Observable.Throw<AuthenticationResult>(new ForbiddenException(response)));
+            var browser = Substitute.For<IVisualStudioBrowser>();
+            var loginViewModel = new LoginToGitHubViewModel(repositoryHosts, browser);
+
+            loginViewModel.Login.Execute(null);
+
+            Assert.True(loginViewModel.ShowLogInFailedError);
+            Assert.Equal("Make sure to use your password and not a Personal Access token to log in.",
+                loginViewModel.LoginFailedMessage);
+        }
+    }
+
     public class TheSignupCommand : TestBaseClass
     {
         [Fact]