How does it work using ASP.NET FormAuthentication

Question

Our ASP.NET website is using FormAuthentication. After login success, it will add a cookie to client side. Here is the code.

 FormsAuthenticationTicket ticket = new FormsAuthenticationTicket(1,
 username,
 DateTime.Now,
 expiration,
 remember,
 roles,
 FormsAuthentication.FormsCookieName);

 HttpCookie authCookie = new HttpCookie(FormsAuthentication.FormsCookieName, FormsAuthentication.Encrypt(ticket));

 Response.Cookies.Add(authCookie);

Then I can see that a cookie with name .ASPXAUTH is created in client browser. Next time, when I visit the website, I can see that HttpContext.Current.Request.IsAuthenticated is marked into true automatically. I guess ASP.NET decrypt the cookie and get the user information.

How can I debug this process? I want to see the source code to find out how HttpContext.Current.Request.IsAuthenticated is assgined into true.