I have a little doubt, can you instantiate in some way (or something), to call a Panel, updatePanel, div from a master page from another normal page?
Let me explain myself: in the master page I have an updatePanel (inside a panel) with a small login form, and I would like to call it from any other page of my site.
I'm working with asp.net c # webForms.
The question is not very clear to me, but depending on how you structure your master page, you can use it to make the other pages look the same. If you put a form in the master, it will be shown in the other pages.
You can indicate which is the master in the other pages in the .aspx file of each, at the beginning, through directives, for example:
<%@ Page Language="C#" MasterPageFile="~/MiMaster.Master" AutoEventWireup="true" CodeBehind="MiPagina.aspx.cs" Inherits="MiProyecto.MiPagina" %>
However, you can not access the controls, forms, etc, of the master from the other pages in your .cs files, the code associated with your login form in the master will be executed in your .cs file, not in the pages that have it as master.
If you want to be able to invoke the login when the session is over, for example, you can create a login page that does not inherit from the master, customize it to your liking and invoke it whenever you detect that a user session It's over, and leave the master for menus, banners, background images, etc.
If you want to use yes or if you control your login on all the pages, you can create a custom web control, add it to your project and call it on your pages, for example:
<aspSample:ControlLogin ID="MiControlLogin" runat="server"></aspSample:ControlLogin>
However, the logic of communication with the database server, etc., must be handled for each of the pages where it is used.