VCST-872: add non-functional subscription (#542)

src/VirtoCommerce.ExperienceApiModule.Core/Schemas/SubscriptionSchema.cs

@@ -0,0 +1,47 @@
+using System;
+using System.Reactive.Linq;
+using System.Threading.Tasks;
+using GraphQL;
+using GraphQL.Resolvers;
+using GraphQL.Subscription;
+using GraphQL.Types;
+using Microsoft.AspNetCore.Authorization;
+using VirtoCommerce.ExperienceApiModule.Core.Extensions;
+using VirtoCommerce.ExperienceApiModule.Core.Infrastructure;
+using VirtoCommerce.ExperienceApiModule.Core.Infrastructure.Authorization;
+using VirtoCommerce.Platform.Security.Authorization;
+
+namespace VirtoCommerce.ExperienceApiModule.Core.Schemas
+{
+    public class SubscriptionSchema(IAuthorizationService authorizationService) : ISchemaBuilder
+    {
+        public void Build(ISchema schema)
+        {
+            var pingType = new EventStreamFieldType
+            {
+                Name = "ping",
+                Type = typeof(StringGraphType),
+                Resolver = new FuncFieldResolver<string>(Resolve),
+                AsyncSubscriber = new AsyncEventStreamResolver<string>(Subscribe),
+            };
+            schema.Subscription.AddField(pingType);
+        }
+
+        private string Resolve(IResolveFieldContext context)
+        {
+            return context.Source as string;
+        }
+
+        private async Task<IObservable<string>> Subscribe(IResolveEventStreamContext context)
+        {
+            var authorizationResult = await authorizationService.AuthorizeAsync(context.GetCurrentPrincipal(), null, new PermissionAuthorizationRequirement(string.Empty));
+            if (!authorizationResult.Succeeded)
+            {
+                throw AuthorizationError.Forbidden();
+            }
+
+            // reserved for future use
+            return Observable.Never<string>();
+        }
+    }
+}