Enable MicroBuild Signing in CoreClr 1.0.0 (#17940)

* Enable MicroBuild Signing in CoreClr 1.0.0

* Remove private pattern

Author: wtgodbe

src/publish.proj

@@ -23,6 +23,28 @@
     <PublishPattern Condition="'$(PublishPattern)' == ''">$(PackagesBinDir)**\*.nupkg</PublishPattern>
   </PropertyGroup>
 
+  <PropertyGroup>
+    <PackageDownloadDirectory Condition="'$(DownloadDirectory)' == ''">$(PackagesDir)AzureTransfer\$(ConfigurationGroup)</PackageDownloadDirectory>
+    <FinalPublishPattern>$(PackageDownloadDirectory)\**\*.nupkg</FinalPublishPattern>
+    <FinalSymbolsPackagesPattern>$(PackageDownloadDirectory)\**\*.symbols.nupkg</FinalSymbolsPackagesPattern>
+    <!-- The SignFiles target needs OutDir to be defined -->
+    <OutDir>$(PackageDownloadDirectory)</OutDir>
+  </PropertyGroup>
+
+  <Target Name="GetPackagesToSign">
+    <ItemGroup>
+      <FilesToSign Include="$(FinalPublishPattern)" Exclude="$(FinalSymbolsPackagesPattern)">
+        <Authenticode>NuGet</Authenticode>
+      </FilesToSign>
+    </ItemGroup>
+    <Message Importance="High" Text="Attempting to sign package '%(FilesToSign.Identity)'" />
+  </Target>
+
+  <Target Name="SignPackages"
+          Condition="'$(SkipSigning)' != 'true' and '$(SignType)' != 'public'"
+          DependsOnTargets="GetPackagesToSign;SignFiles">
+  </Target>
+
   <Target Name="CreateContainerName"
           DependsOnTargets="CreateVersionFileDuringBuild"
           Condition="'$(ContainerName)' == ''">