Getting HTML form input with C#

I am having a problem getting HTML input values using C# for a Login page. I have had luck using just a regular ASP element, but not so much with pure HTML.

I am trying to have the C# grab the username input and password from the html form to then send as a string to a MySQL db proc. If the username/password combination does not exist, I am trying to redirect back to the Login.aspx page and if it does "google.com". The username and password are also saved in a session.

My HTML looks like the following:

<form action="Login.aspx.cs" runat="server" method="post">
            <input type="text" name="un" pattern="a[0-9]{6}" required="required" placeholder="a000000"/><br />
            <input type="password" name="pw"  required="required" /><br />
            <asp:Button ID="Button1" Text="text" runat="server" OnClick="Login1_Authenticate" />
</form>

And my C# looks like the following:

using System;
using System.Data;
using System.Data.SqlClient;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;


public partial class Login : System.Web.UI.Page
{
    int status;
    int role;
    protected void Page_Load(object sender, EventArgs e)
    {

    }

    public void Login1_Authenticate(object sender, AuthenticateEventArgs e)
    {

        //// create an open connection
        SqlConnection conn =
            new SqlConnection("Data Source=MachineName;"
            + "Initial Catalog=DBName;"
            + "User ID=Usr ;Password=Password");

        conn.Open();

        string userName = Page.Request.Form["un"].ToString();
        string pw = Page.Request.Form["pw"].ToString();
        //userName = Convert.ToString(Console.ReadLine());


        //// create a SqlCommand object for this connection
        SqlCommand command = conn.CreateCommand();
        command.CommandText = "EXEC dbo.SP_CA_CHECK_USER @USER_ID = '" + userName + "', @PASSWORD = '" + pw + "'";
        command.CommandType = CommandType.Text;

        //// execute the command that returns a SqlDataReader
        SqlDataReader reader = command.ExecuteReader();

        //// display the results
        while (reader.Read())
        {
            status = reader.GetInt32(0);
        }

        //// close first reader
            reader.Close();


            if (status == 0)
            {
                //login
                Session["userID"] = userName;
                command.CommandText = "EXEC dbo.SP_CA_RETURN_USER_ROLE @USER_ID = '" + userName + "'";
                reader = command.ExecuteReader();
                while (reader.Read())
                {
                    role = reader.GetInt32(0);
                }

                Session["roleID"] = role;

                if (Session["userID"] != null)
                {
                    string userID = (string)(Session["userID"]);
                    // string roleID = (string)(Session["roleID"]);
                }
                Response.Redirect("http://www.microsoft.com");
            }
            else
            {
                //wrong username/password
                Response.Redirect("http://www.microsoft.com");
            }



            // close the connection
            reader.Close();
            conn.Close();

    }
}