See if user is part of Active Directory group in C# + Asp.net

Question

I need a way to see if a user is part of an active directory group from my .Net 3.5 asp.net c# application.

I am using the standard ldap authentication example off o

Answer 1

Nick Craver's solution doesn't work for me in .NET 4.0. I get an error about an unloaded AppDomain. Instead of using that, I used this (we only have one domain). This will check groups of groups as well as direct group membership.

using System.DirectoryServices.AccountManagement;
using System.Linq;

...

using (var ctx = new PrincipalContext(ContextType.Domain, yourDomain)) {
    using (var grp = GroupPrincipal.FindByIdentity(ctx, IdentityType.Name, yourGroup)) {
        bool isInRole = grp != null && 
            grp
            .GetMembers(true)
            .Any(m => m.SamAccountName == me.Identity.Name.Replace(yourDomain + "\\", ""));
    }
}