asp.net - How to do Web Service Authorization in this code?

Question

Am thinking of using this bit of code here to call a WebService and have it populate into a JS file as well for calling the Webservice Methods.

<asp:ScriptManager runat="server" ID="scriptManagerId">
          <Scripts>
              <asp:ScriptReference Path="CallWebServiceMethods.js" />
          </Scripts>
          <Services>
              <asp:ServiceReference  Path="http://ws.idssasp.com/members.asmx?wsdl" />
          </Services>
</asp:ScriptManager>

But the problem is the webservice needs a username and password before it will return anything. How do I use this bit of code for a username and password to Authenticate it?