getCert.cs

private static X509Certificate2 GetIISExpressCertificateFromLocalStore()
{
    // http://stackoverflow.com/questions/1742938/how-to-solve-could-not-establish-trust-relationship-for-the-ssl-tls-secure-chan
    ServicePointManager.ServerCertificateValidationCallback += (se, cert, chain, sslerror) => true;

    var store = new X509Store(StoreLocation.CurrentUser);

    store.Open(OpenFlags.ReadOnly);

    var certs = store.Certificates.Find(X509FindType.FindBySubjectName, "localhost", false);

    if (certs.Count == 0)
    {
        throw new Exception($"Cannot find localhost cert");
    }

    store.Close(); // Using block was failing - but its idisposable

    // By now we have at least one cert that matches thumb - use it
    // If i get 2 and it starts using the wrong cert - Fix the store...
    return certs[0];
}

main.cs

static void Main(string[] args)
{
    var authCert = new X509Certificate2("J:\\Export.cer");
    var tlsCert = GetIISExpressCertificateFromLocalStore();

    var requestHandler = new WebRequestHandler();

    requestHandler.ClientCertificates.Add(authCert);
    requestHandler.ClientCertificates.Add(tlsCert);
    requestHandler.ServerCertificateValidationCallback += (sender, certificate, chain, errors) => true;

    var client = new HttpClient(requestHandler)
    {
        BaseAddress = new Uri("https://localhost:44365/"),
    };

    var response = client.GetAsync("api").Result; // Ew
    var responseContent = response.Content.ReadAsStringAsync().Result; // Ew

    Console.WriteLine(responseContent);
}