How to login in any website programmatically?

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C#

Hello,
I want to enter the username and password in a website programmatically. I tried my self by some code. could not get success. I have done a lot of googling but could not get proper answer. Anybody who knows this, please help me.

What I have tried:

private void button1_Click(object sender, EventArgs e)
        {

            webBrowser1.Navigate(webBrowser1.Url);
            while (webBrowser1.ReadyState != WebBrowserReadyState.Complete)
            {
                Application.DoEvents();
            }
            webBrowser1.Document.GetElementById("username").InnerText=textBox1.Text;
            webBrowser1.Document.GetElementById("password").InnerText = textBox2.Text;
            webBrowser1.Document.GetElementById("submit").InvokeMember("LOGIN");
              
        }