How do I validate the username and password with the ones from database and then redirect from ajax if they are?

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C#

Javascript

MySQL

jQuery

Hello! So i have a login form with user, pass and a button for login. On this button i want to put a JavaScript listener and when clicked to fire a $.ajax() function who sends
a request to the login page and then return a json response with 2 fields: error(failed) and msg(user/pass ok). When the ajax ends, the success function must display on the page the value from msg and if there is no error redirect to home page.
i suppose that in some way i need to verify the user/pass with what i have in the database, i just don't know how to do it.
i currently use sessions for my authentications and it works just fine but now my new task is to change it.
i tried something below the problem is i don't know how to do the validation with the database to see if the user and password are correct.
please help me with some ideas.
Thank you

What I have tried:

This is my table
 <table style="background-color:#f1f1f1">
             <tr>
                 <td><asp:Label runat="server" ID="lbl1" Font-Bold="true" ForeColor="Red"/></td>
             </tr>
           
             <tr>
                 <td><asp:Label runat="server">Username</asp:Label></td>
                 <td><asp:TextBox runat="server" ID="txtUser" placeholder="Username"/></td>
                 <td><asp:RequiredFieldValidator ID="rfvUser" runat="server" ControlToValidate="txtUser" ErrorMessage="*" ForeColor="Red" Font-Bold="true"  ValidationGroup="LoginInfo"/></td>
             </tr>
             <tr>
                 <td><asp:Label runat="server">Password</asp:Label></td>
                 <td><asp:TextBox runat="server" ID="txtPass" TextMode="Password" placeholder="Password"/></td>
                 <td><asp:RequiredFieldValidator ID="rfvPass" runat="server" ControlToValidate="txtPass" ErrorMessage="*" ForeColor="Red" Font-Bold="true"  ValidationGroup="LoginInfo"/></td>
             </tr>
             
             <tr >
                 <td></td>
                 <td><asp:Button runat="server" Text="Login" ID="btnLogin" CssClass="button" Width="210"  OnClick="btnLogin_Click" ValidationGroup="LoginInfo"/></td>
             </tr>
</table>

Here what i have been trying :

<script>
$(document).ready(function myfunction () {
                $('#btnLogin').click(function () {
                    var user = $('#txtUser').val();
                    var pass = $('#txtPass').val();

                    if (user != '' && pass != '') {
                        $.ajax({
                            type: "POST",
                            contentType: "application/json; charset=utf-8",
                            url: "Login.aspx/InsertData",
                            data: {user: txtUser, pass: txtPass},
                            dataType: "json",
                            success: function (data) {
                                var obj = data.d;
                                if (obj == 'true') {
                                    $('#txtUser').val('');
                                    $('#txtPass').val('');
                                    $('#lbl1').html("Login Successfully");
                                    // window.location = "Default.aspx";??
                                }
                            },
                            error: function (result) {
                                $('#lbl1').html("Wrong username or password");
                               
                            }
                        });
                    }
                    else {
                        $('#lbl1').html("Please fill all fields");
                        return false;
                    }
                });
                });
          
        </script>

and in my aspx.cs maybe something like :

[WebMethod]
   public static string InsertData(string user, string pass)
   {
       string msg = string.Empty;
       using (MySqlConnection conn = new MySqlConnection(WebConfigurationManager.ConnectionStrings["myConnectionString"].ConnectionString))
       {
           using (MySqlCommand cmd = new MySqlCommand("select * from useri where Username=@Username and Password=@Password", conn))
           {
               conn.Open();
               cmd.Parameters.AddWithValue("@Username", user);
               cmd.Parameters.AddWithValue("@Password", pass);
               int i = cmd.ExecuteNonQuery();
               conn.Close();
               if(i==1)
               {
                   msg = "true";
               }
               else
               {
                   msg = "false";
               }
           }
       }
       return msg;

   }