// Create the NetworkAuthenticationHandler with credentials
var networkAuthenticationHandler = new NetworkAuthenticationHandler
{
    UriMatcher = uri => uri.Host.Contains("ident.me"), // Only apply for the specific host
    Credentials = new NetworkCredential("your_proxy_username", "your_proxy_password")
};

// Add the authentication credentials to the network request
var networkInterceptor = driver.Manage().Network;
networkInterceptor.AddAuthenticationHandler(networkAuthenticationHandler);