How to programmatically fill out a form on a website?

Question

Visual Basic

On the site b98300b7.beget.tech, I posted a form that records the data entered in 2 text fields - login and password. (Later I will delete this form). I need to let's say that by pressing a button (on a form in my program) data were entered into these 2 fields on the site and the "Login" button was pressed.
Please do not post links to other similar topics, it is not very clear there.

Answer 1

I actually found the answer to my own question:

Private Sub Button5_Click(sender As Object, e As EventArgs) Handles Button5.Click
        Dim AuthThread As New System.Threading.Thread(AddressOf DataAuth)
        AuthThread.IsBackground = True
        AuthThread.Start()
    End Sub
    Sub DataAuth()
        Invoke(Sub() WebBrowser1.Document.GetElementById("id_username").InnerText = "Login")
        Threading.Thread.Sleep(50)
        Invoke(Sub() WebBrowser1.Document.GetElementById("id_password").InnerText = "Password")
        Threading.Thread.Sleep(300)
        Invoke(Sub()
                   Dim buttons As HtmlElementCollection = WebBrowser1.Document.GetElementsByTagName("input")
                   For Each btn As HtmlElement In buttons
                       If btn.GetAttribute("classname") = "button-green" Then
                           btn.InvokeMember("Click")
                       End If
                   Next
               End Sub)
    End Sub