MVC - Find Controllers With (Authorize) Attributes Using Reflection In C# Or Build Dynamic Site.Master Menus?

I'm currently writing a web app in ASP.NET MVC 1.0 (although I do have MVC 2.0 installed on my PC, so I'm not exactly restricted to 1.0) -- I've started with the standard MVC project which has your basic "Welcome to ASP.NET MVC" and shows both the [Home] tab and [About] tab in the upper-right corner. Pretty standard, right? I've added 4 new Controller classes, let's call them "Astronomer", "Biologist", "Chemist", and "Physicist". Attached to each new controller class is the [Authorize] attribute. For example, for the BiologistController.cs

[Authorize(Roles = "Biologist,Admin")]
public class BiologistController : Controller
{
public ActionResult Index() { return View(); }
}

These [Authorize] tags naturally limit which user can access different controllers depending on Roles, but I want to dynamically build a Menu at the top of my website in the Site.Master Page based on the Roles the user is a part of. So for example, if "JoeUser" was a member of Roles "Astronomer" and "Physicist", the navigation menu would say:

[Home] [Astronomer] [Physicist]
[About]

And naturally, it would not list links to "Biologist" or "Chemist" controller Index page. Or if "JohnAdmin" was a member of Role "Admin", links to all 4 controllers would show up in the navigation bar. Ok, you prolly get the idea... Now for the real question... Starting with the answer from this StackOverflow topic about Dynamic Menu building in ASP.NET, I'm trying to understand how I would fully implement this. (I'm a newbie and need a little more guidance, so please bare with me.) The answer proposes Extending the Controller class (call it "ExtController") and then have each new WhateverController inherit from ExtController.

My conclusion is that I would need to use Reflection in this ExtController Constructor to determine which Classes and Methods have [Authorize] attributes attached to them to determine the Roles. Then using a Static Dictionary, store the Roles and Controllers/Methods in key-value pairs. I imagine it something like this:

public class ExtController : Controller
{
protected static Dictionary<Type,List<string>> ControllerRolesDictionary;
protected override void OnActionExecuted(ActionExecutedContext filterContext)
{
// build list of menu items based on user's permissions, and add it to ViewData
IEnumerable<MenuItem> menu = BuildMenu();
ViewData["Menu"] = menu;
}
private IEnumerable<MenuItem> BuildMenu()
{
// Code to build a menu
SomeRoleProvider rp = new SomeRoleProvider();
foreach (var role in rp.GetRolesForUser(HttpContext.User.Identity.Name))
{
}
}
public ExtController()
{
// Use this.GetType() to determine if this Controller is already in the Dictionary
if (!ControllerRolesDictionary.ContainsKey(this.GetType()))
{
// If not, use Reflection to add List of Roles to Dictionary
// associating with Controller
}
}
}

Is this doable? If so, how do I perform Reflection in the ExtController constructor to discover the [Authorize] attribute and related Roles (if any) ALSO! Feel free to go out-of-scope on this question and suggest an alternate way of solving this "Dynamic Site.Master Menu based on Roles" problem. I'm the first to admit that this may not be the best approach.