Setting cookies to httpClient of Asp.Net Core TestServer

I,m testing ASP.NET Core app with TestServer, and there are controllers that require cookie auth. I've created test server instance like this:

_testServer = new TestServer(new WebHostBuilder()
            .UseEnvironment(CustomEnvironments.Test)
            .UseContentRoot(currentDirectory)                
            .UseStartup<Web.Startup>()
            .UseUrls("http://localhost/"));

ApiClient = _testServer.CreateClient();

and now I have to add auth cookie, but it is ignored by server. If the client could be created directly I could pass HttpClientHandler to constractor and set UseCookies to false, and it works, but I can't access the handler when I get client from test server. Is there a way to add auth cookies to test client?