You could still do today what you did in classic ASP. You could, client side or server side, generate input controls and then at the server after a postback loop through the items in Request.Form, finding the ones you need and use their values.
Alternativelly, you can create controls programmatically during Init as explained here
Finally, you could look into ASP.NET MVC that lets you work much closer to the form and its controls, giving you a much more direct way to interact with them.
Hope this helps,