How to add 2 authentication headers in a HTTP request using C# .NET Framework

So this is just a simple example that just pulls in the google homepage information. But what I would like to do is get data from a rest API using HttpClient in C# .NET Framework but the issue is I couldn't figure out how to add in 2 authentication headers, the two parameters should be for like a API-Key and an API-Secret-Key. Here is the code I have right now.

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Net.Http;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace Reporting
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void btnSubmit_Click(object sender, EventArgs e)
        {
            string StartDate = dtpStartDate.Text;
            string EndDate = dtpEndDate.Text;
            Main();

            async Task Main()
            {
                try
                {
                    var client = new HttpClient();
                    // Call asynchronous network methods in a try/catch block to handle exceptions.
                    HttpResponseMessage response = await client.GetAsync("https://www.google.com");
                    response.EnsureSuccessStatusCode();
                    string responseBody = await response.Content.ReadAsStringAsync();
                    // Above three lines can be replaced with new helper method below
                    // string responseBody = await client.GetStringAsync(uri);
                    label1.Text = responseBody;
                }
                catch (Exception ex)
                {
                    label2.Text = ex.ToString();
                    //throw ex;
                }
            }
        }
    }
}