Update to ASP.NET 5 preview 8

Update to preview 8 of ASP.NET 5.

Author: martincostello

Directory.Packages.props

@@ -4,10 +4,10 @@
     <PackageVersion Include="JetBrains.Annotations" Version="2020.1.0" />
     <PackageVersion Include="JustEat.HttpClientInterception" Version="3.0.0" />
     <PackageVersion Include="MartinCostello.Logging.XUnit" Version="0.1.0" />
-    <PackageVersion Include="Microsoft.AspNetCore.Authentication.Google" Version="5.0.0-preview.7.*" />
-    <PackageVersion Include="Microsoft.AspNetCore.Authentication.Twitter" Version="5.0.0-preview.7.*" />
-    <PackageVersion Include="Microsoft.AspNetCore.Mvc.Testing" Version="5.0.0-preview.7.*" />
-    <PackageVersion Include="Microsoft.AspNetCore.TestHost" Version="5.0.0-preview.7.*" />
+    <PackageVersion Include="Microsoft.AspNetCore.Authentication.Google" Version="5.0.0-preview.8.*" />
+    <PackageVersion Include="Microsoft.AspNetCore.Authentication.Twitter" Version="5.0.0-preview.8.*" />
+    <PackageVersion Include="Microsoft.AspNetCore.Mvc.Testing" Version="5.0.0-preview.8.*" />
+    <PackageVersion Include="Microsoft.AspNetCore.TestHost" Version="5.0.0-preview.8.*" />
     <PackageVersion Include="Microsoft.CodeAnalysis.FxCopAnalyzers" Version="3.3.0" />
     <PackageVersion Include="Microsoft.IdentityModel.Protocols.OpenIdConnect" Version="6.6.0" />
     <PackageVersion Include="Moq" Version="4.14.5" />

global.json

@@ -1,6 +1,6 @@
 {
   "tools": {
-    "dotnet": "5.0.100-preview.7.20366.6"
+    "dotnet": "5.0.100-preview.8.20417.9"
   },
 
   "msbuild-sdks": {

samples/Mvc.Client/Controllers/AuthenticationController.cs

@@ -40,7 +40,7 @@ public async Task<IActionResult> SignIn([FromForm] string provider)
 
         [HttpGet("~/signout")]
         [HttpPost("~/signout")]
-        public IActionResult SignOut()
+        public override SignOutResult SignOut()
         {
             // Instruct the cookies middleware to delete the local cookie created
             // when the user agent is redirected from the external identity provider

src/AspNet.Security.OAuth.VisualStudio/VisualStudioAuthenticationDefaults.cs

@@ -17,7 +17,7 @@ public static class VisualStudioAuthenticationDefaults
         /// <summary>
         /// Default value for <see cref="AuthenticationScheme.Name"/>.
         /// </summary>
-        public const string AuthenticationScheme = "Visual Studio Online";
+        public const string AuthenticationScheme = "VisualStudioOnline";
 
         /// <summary>
         /// Default value for <see cref="AuthenticationScheme.DisplayName"/>.