wcf web service only generates async methods when consuming it in xamarin.forms app - wcf

Question

i am trying to connect my xamarin.forms app to sql server. i know that i have to use a webservice to do that. i am using wcf web service. the problem is that i only got async methods after adding it as a connected service to my app. like the problem in this question: Xamarin.Forms Add Connected Service on WCF only generated async method the thing is i can't use its answer because i don't have the generate synchronous operations option, i found another answer in this: WCFclient operation only Async .Net core 2.0 but i really still don't know how to use the async methods. like how do i get the result of the operation to perform my login when clicking a button. this is my code for the wcf webservice:
Iuserlogin.cs:
[ServiceContract]
public interface Iuserlogin
{
[OperationContract]
[WebInvoke(BodyStyle = WebMessageBodyStyle.Bare, ResponseFormat = WebMessageFormat.Json, Method = "POST")]
DataTable login(string username, string pass);
}
userlogin.svc.cs:
public class userlogin : Iuserlogin
{
public DataTable login(string username, string pass)
{
DataTable dt = new DataTable();
dt.TableName = "summary_req";
SqlConnection con = new SqlConnection("server=DESKTOP-CPOJ94O\\MSSQLSERVER1;database=users;integrated security=true");
con.Open();
SqlCommand cmd = new SqlCommand("SELECT username, password FROM hjk where CONVERT(VARCHAR, username)=#username and CONVERT(VARCHAR, password)=#password", con);
cmd.Parameters.AddWithValue("#username", username);
cmd.Parameters.AddWithValue("#password", pass);
SqlDataAdapter da = new SqlDataAdapter(cmd);
da.Fill(dt);
return dt;
}
}
}
this is my trial to use the async functions in my app:
MainPage.xaml.cs:
public partial class MainPage : ContentPage
{
public MainPage()
{
InitializeComponent();
}
private void SignIn_Clicked(object sender, EventArgs e)
{
ServiceReference1.IuserloginClient cs = new ServiceReference1.IuserloginClient();
string user_name = username.Text;
string pass = password.Text;
ServiceReference1.loginRequest loginreq= new ServiceReference1.loginRequest(user_name, pass);
ServiceReference1.loginResponse response = cs.loginAsync(user_name, pass).Result;
}
}
}
i don't know what to do next. how do i continue to know if the user can login or not. how do i get a datatable result from the wcf functions.
thanks in advance.