Filter Allowed Document Types and Templates in Umbraco

MyApplication.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Net.Http;
using System.Threading;
using System.Threading.Tasks;
using System.Web;
using Umbraco.Core;
using Umbraco.Web;
using Umbraco.Web.Models.ContentEditing;

namespace WebApplication2.App_Code
{
    public class MyApplication : ApplicationEventHandler
    {
        protected override void ApplicationStarting(UmbracoApplicationBase umbracoApplication, ApplicationContext applicationContext)
        {
            System.Web.Http.GlobalConfiguration.Configuration.MessageHandlers.Add(new MyApiHandler());
        }
    }

    public class MyApiHandler : System.Net.Http.DelegatingHandler
    {
        protected override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
        {
            var user = UmbracoContext.Current.Security.CurrentUser;

            switch (request.RequestUri.AbsolutePath.ToLower())
            {
                case "/umbraco/backoffice/umbracoapi/contenttype/getallowedchildren":
                    return FilterAllowedContentTypes(request, cancellationToken, user);
                case "/umbraco/backoffice/umbracoapi/content/getbyid":
                    return FilterAllowedTemplates(request, cancellationToken, user);
                default:
                    return base.SendAsync(request, cancellationToken);
            }
        }

        private Task<HttpResponseMessage> FilterAllowedTemplates(HttpRequestMessage request, CancellationToken cancellationToken, Umbraco.Core.Models.Membership.IUser user)
        {
            return base.SendAsync(request, cancellationToken)
                    .ContinueWith(task =>
                    {
                        var response = task.Result;
                        try
                        {
                            var data = response.Content;
                            var content = ((ObjectContent)(data)).Value as ContentItemDisplay;
                            var templates = content.Properties.FirstOrDefault(x => x.Alias == "_umb_template");

                            if (templates != null && templates.Config.ContainsKey("items"))
                            {
                                var allowedTemplates = ((Dictionary<string, string>)templates.Config["items"]);
                                
                                // Replace this with your filtering logic
                                if (user.Name == "Danny Drogt")
                                {
                                    if (allowedTemplates.ContainsKey("umbTextPage"))
                                    {
                                        allowedTemplates.Remove("umbTextPage");
                                    }
                                }
                            }
                        }
                        catch (Exception ex)
                        {
                            // Log
                        }

                        return response;
                    });
        }

        private Task<HttpResponseMessage> FilterAllowedContentTypes(HttpRequestMessage request, CancellationToken cancellationToken, Umbraco.Core.Models.Membership.IUser user)
        {
            return base.SendAsync(request, cancellationToken)
                    .ContinueWith(task =>
                    {
                        var response = task.Result;
                        try
                        {
                            var data = response.Content;
                            var allowedTemplates = ((ObjectContent)(data)).Value as IList<ContentTypeBasic>;

                            if (allowedTemplates != null)
                            {
                                // Replace this with your filtering logic
                                if (user.Name == "Danny Drogt")
                                {
                                    allowedTemplates.Clear();
                                }
                            }
                        }
                        catch (Exception ex)
                        {
                            // Log
                        }

                        return response;
                    });
        }
    }
}

This is downright amazing. So happy that I stumbled on this!