Add missing reference

Author: MackinnonBuck

src/Http/Authentication.Core/src/Microsoft.AspNetCore.Authentication.Core.csproj

@@ -14,6 +14,7 @@
     <Reference Include="Microsoft.AspNetCore.Authentication.Abstractions" />
     <Reference Include="Microsoft.AspNetCore.Http" />
     <Reference Include="Microsoft.AspNetCore.Http.Extensions" />
+    <Reference Include="Microsoft.Extensions.Diagnostics" />
   </ItemGroup>
 
   <ItemGroup>