我想我明白了。

请随时进行改进并重新发布：

[AttributeUsage(AttributeTargets.Class, AllowMultiple = false, Inherited = true)]
public class ARQAuthorize : AuthorizeAttribute
{
    protected override bool AuthorizeCore(HttpContextBase httpContext)
    {
        bool allowToUse = false;
        IPrincipal user = httpContext.User;
        if (!user.Identity.IsAuthenticated)
        {
            return false;
        }
        else{
        try
        {
           Arq.Core.DAL.ArqContext c = new ArqContext();
           if (c.Users.Where(u => u.UserName.ToUpper() == user.Identity.Name.ToUpper()).FirstOrDefault().role.RoleDescription == "ADMINS")
           {
               allowToUse = true;
           }
        }
        catch (Exception)
        {

            allowToUse = false;
        }
        }          
            return allowToUse;

    }

}