How should my method look like for automatic authentication?

See more:

C#

SQL

WPF

MVVM

Hello,

I have a login form which has only one field for the password.My approach is using an RFID reader that reads values from the NFC tag and display it in a textbox.I have passwordbox that fills up with the SN of the card when the user swipes the card of the card reader.This happening,in the passwordbox will apear the SN and I want to check the SN with the values from the db.If the value exists,the user will automatically enter in the system without pressing any button or doing any sort of action.I have my method for now that checks the value,but i don't know how to do it so that it will automatically log in the user into the system.I've searched for examples in hope that I will find some relevant connection to what I have,but unfortunately I couldn't find anything suitable in my case.My RFID reader is working perfectly,my basic method works fine.Could someone please give me an example of how this should be made?I'm using WPF with MVVM and db first.Thank you in advance!

What I have tried:

This is my basic method for log in:

public void SubmitButton(object param)
     {

         SqlConnection conn = new SqlConnection(@"Data Source=(LocalDB)\MSSQLLocalDB;AttachDbFilename=C:\Users\User\source\repos\VIAApp2Demo\VIAApp2Demo\DB\DatabaseStudents.mdf;Integrated Security=True;Connect Timeout=30");
         try
         {


             if (conn.State == System.Data.ConnectionState.Closed)
                 conn.Open();
             String query = "SELECT COUNT (*) FROM Login where pwd=@pwd";
             SqlCommand cmd = new SqlCommand(query, conn);
             cmd.CommandType = CommandType.Text;



             SqlParameter Pwd = cmd.Parameters.AddWithValue("@pwd", SqlDbType.Int);
             //cmd.Parameters["@pwd"].Value = _pwd.pwd;
             cmd.Parameters["@pwd"].Value = TestPassword;
             if (Pwd.Value == null)
             {
                 Pwd.Value = DBNull.Value;
             }

             int count = Convert.ToInt32(cmd.ExecuteScalar());
             if (count > 0)

             {
                 MainWindow main = new MainWindow();
                 main.Show();

             }
             else
             {
                 MessageBox.Show("Password is incorrect!");
             }

         }

         catch (Exception ex)
         {
             MessageBox.Show(ex.Message);
         }
         finally
         {
             conn.Close();
         }
     }