Custom IPrincipal with Forms Authentication in ASP.NET MVC

This should be simple, but I simply cannot figure it out after all my googling. Here's what I want. I have a custom Users table (no roles at the moment) that I'd like to authorize against. For this I'll have to implement a custom Membership Provider which I've already done. My question is though, how do I go about setting a custom IPrincipal to the HttpContext.Current.User? Where should that happen? Let's say I have the following setup:

public class CustomMembershipProvider : MembershipProvider
{
   private IUserRepository _repository;

   public CustomMembershipProvider(IUserRepository repository)
   {
      _repository = repository;
   }

   public override bool ValidateUser(string username, string password)
   {
      //check user repository 
   }

   //additional methods omitted for brevity 
}

I then have a custom user class the implements IPrincipal and IIdentity

 public class CustomUser : IPrincipal
    {
        public CustomUser(string name, int userId, string additionalInfo)
        {
            Identity = new Cu开发者_JS百科stomIdentity(name, userId, additionalInfo);
        }

        public IIdentity Identity { get; private set; }

        public bool IsInRole(string role)
        {
            return true;
        }
    }

    public class CustomIdentity : IIdentity
    {
        public CustomIdentity(string name, int userId, string additionalInfo)
        {
            Name = name;
            UserId = userId;
            AdditionalInfo = additionalInfo;
        }

        public string Name { get; private set; }

        public string AuthenticationType
        {
            get { return "CustomAuth"; }
        }

        public bool IsAuthenticated
        {
            get { return !String.IsNullOrEmpty(Name); }
        }

        public int UserId { get; private set; }
        public string AdditionalInfo { get; private set; }
    }

So my question is, where is the correct place to set the Context.User to an instance of this custom user? Do I need a custom Authorize Attribute? If so, what would that look like?

I suggest using a custom controller base class for all your controllers

Then, in OnAuthorization, call

protected override void OnAuthorization(System.Web.Mvc.AuthorizationContext filterContext)
{
    // Actual Authentication
    HttpContext.User = user; 
    Thread.CurrentPrincipal = user;
    base.OnAuthorization(filterContext);
}

I'm not entirely sure how to invoke the membership provider because I'm doing it manuallt, but I think you have static access to Membership.Provider to perform the actual object construction.

Do I need a custom Authorize Attribute?

No. Notice the difference of authentication and authorization: authentication establishes the user's identity in your system. Authorization allows or denies a specific request. Hence, AuthorizeAttribute also has a Roles parameter to allow an action to be called only by certain users.