I am developing an Asp.Net web application that will access data in a list on a SharePoint 2010 server. Can anyone tell me how do I authenticate a user against SharePoint using the server side object model? What are the different possible methods that I can use use to achieve this? The question may be dumb as I am really new to SharePoint and I'm stuck with it. I know how to do it using ASP.NET web services exposed by sharepoint.
All users are by default Authenticated in SharePoint (unless you are using a zone with anonymous access). You don't have to do anything.
Impersonation, if that is what you actually mean, is done in the same way as in plain ol' ASP.NET.