auth.cs

INetwork networkInterceptor = driver.Manage().Network;
NetworkAuthenticationHandler handler = new NetworkAuthenticationHandler()
{
    UriMatcher = (url) => url.Host == "the-internet.herokuapp.com" && url.PathAndQuery.Contains("basic_auth"),
    Credentials = new PasswordCredentials("admin", "admin")
};

await networkInterceptor.StartMonitoring();

driver.Url = "http://the-internet.herokuapp.com/basic_auth";
string bodyText = driver.FindElement(By.CssSelector("body")).Text;
if (bodyText.Contains("Not authorized"))
{
    Console.WriteLine("Authentication Denial PASSED");
}
else
{
    Console.WriteLine("Authentication Denial FAILED");
}

networkInterceptor.AddAuthenticationHandler(handler);
driver.Url = "http://the-internet.herokuapp.com/basic_auth";
string text = driver.FindElement(By.CssSelector("h3")).Text;
if (text == "Basic Auth")
{
    Console.WriteLine("Authentication PASSED");
}
else
{
    Console.WriteLine("Authentication FAILED");
}

await networkInterceptor.StopMonitoring();

It is working for me.
Thanks :)