增加支持Autofac的http单元测试

fix issue #I50DRR

OpenAuth.WebApi/Test/AutofacWebApplicationFactory.cs

@@ -0,0 +1,18 @@
+using Microsoft.AspNetCore.Mvc.Testing;
+using Microsoft.Extensions.Hosting;
+
+namespace OpenAuth.WebApi.Test
+{
+    /// <summary>
+    /// Based upon https://github.com/dotnet/AspNetCore.Docs/tree/master/aspnetcore/test/integration-tests/samples/3.x/IntegrationTestsSample
+    /// </summary>
+    /// <typeparam name="TStartup"></typeparam>
+    public class AutofacWebApplicationFactory<TStartup> : WebApplicationFactory<TStartup> where TStartup : class
+    {
+        protected override IHost CreateHost(IHostBuilder builder)
+        {
+            builder.UseServiceProviderFactory(new CustomServiceProviderFactory());
+            return base.CreateHost(builder);
+        }
+    }
+}