Migrated section controller + LanguageTreeController, ApplciationTreeController.

Updated AngularJsonOnlyConfigurationAttribute to be a TypeFilterAttribute, to allow injeciton into the filter.

Note: Left TODO about checking authorization of proxied trees..

src/Umbraco.Web.BackOffice/Controllers/SectionController.cs

@@ -0,0 +1,112 @@
+using System.Collections.Generic;
+using System.Linq;
+using Microsoft.AspNetCore.Mvc.Controllers;
+using Umbraco.Core.Mapping;
+using Umbraco.Core.Models;
+using Umbraco.Core.Services;
+using Umbraco.Web.BackOffice.Controllers;
+using Umbraco.Web.Common.Attributes;
+using Umbraco.Web.Models.ContentEditing;
+using Umbraco.Web.Models.Trees;
+using Umbraco.Web.Security;
+using Umbraco.Web.Services;
+using Umbraco.Web.Trees;
+
+namespace Umbraco.Web.Editors
+{
+    /// <summary>
+    ///     The API controller used for using the list of sections
+    /// </summary>
+    [PluginController("UmbracoApi")]
+    public class SectionController : UmbracoAuthorizedJsonController
+    {
+        private readonly IControllerFactory _controllerFactory;
+        private readonly IDashboardService _dashboardService;
+        private readonly ILocalizedTextService _localizedTextService;
+        private readonly ISectionService _sectionService;
+        private readonly ITreeService _treeService;
+        private readonly UmbracoMapper _umbracoMapper;
+        private readonly IWebSecurity _webSecurity;
+
+        public SectionController(
+            IWebSecurity webSecurity,
+            ILocalizedTextService localizedTextService,
+            IDashboardService dashboardService, ISectionService sectionService, ITreeService treeService,
+            UmbracoMapper umbracoMapper, IControllerFactory controllerFactory)
+        {
+            _webSecurity = webSecurity;
+            _localizedTextService = localizedTextService;
+            _dashboardService = dashboardService;
+            _sectionService = sectionService;
+            _treeService = treeService;
+            _umbracoMapper = umbracoMapper;
+            _controllerFactory = controllerFactory;
+        }
+
+        public IEnumerable<Section> GetSections()
+        {
+            var sections = _sectionService.GetAllowedSections(_webSecurity.GetUserId().ResultOr(0));
+
+            var sectionModels = sections.Select(_umbracoMapper.Map<Section>).ToArray();
+
+            // this is a bit nasty since we'll be proxying via the app tree controller but we sort of have to do that
+            // since tree's by nature are controllers and require request contextual data
+            var appTreeController =
+                new ApplicationTreeController(_treeService, _sectionService, _localizedTextService, _controllerFactory)
+                {
+                    ControllerContext = ControllerContext
+                };
+
+            var dashboards = _dashboardService.GetDashboards(_webSecurity.CurrentUser);
+
+            //now we can add metadata for each section so that the UI knows if there's actually anything at all to render for
+            //a dashboard for a given section, then the UI can deal with it accordingly (i.e. redirect to the first tree)
+            foreach (var section in sectionModels)
+            {
+                var hasDashboards = dashboards.TryGetValue(section.Alias, out var dashboardsForSection) &&
+                                    dashboardsForSection.Any();
+                if (hasDashboards) continue;
+
+                // get the first tree in the section and get its root node route path
+                var sectionRoot = appTreeController.GetApplicationTrees(section.Alias, null, null).Result;
+                section.RoutePath = GetRoutePathForFirstTree(sectionRoot);
+            }
+
+            return sectionModels;
+        }
+
+        /// <summary>
+        ///     Returns the first non root/group node's route path
+        /// </summary>
+        /// <param name="rootNode"></param>
+        /// <returns></returns>
+        private string GetRoutePathForFirstTree(TreeRootNode rootNode)
+        {
+            if (!rootNode.IsContainer || !rootNode.ContainsTrees)
+                return rootNode.RoutePath;
+
+            foreach (var node in rootNode.Children)
+            {
+                if (node is TreeRootNode groupRoot)
+                    return GetRoutePathForFirstTree(groupRoot); //recurse to get the first tree in the group
+                return node.RoutePath;
+            }
+
+            return string.Empty;
+        }
+
+        /// <summary>
+        ///     Returns all the sections that the user has access to
+        /// </summary>
+        /// <returns></returns>
+        public IEnumerable<Section> GetAllSections()
+        {
+            var sections = _sectionService.GetSections();
+            var mapped = sections.Select(_umbracoMapper.Map<Section>);
+            if (_webSecurity.CurrentUser.IsAdmin())
+                return mapped;
+
+            return mapped.Where(x => _webSecurity.CurrentUser.AllowedSections.Contains(x.Alias)).ToArray();
+        }
+    }
+}