Add member routes to API

PluralKit.API/RequiresSystemAttribute.cs

@@ -0,0 +1,23 @@
+using System.Threading.Tasks;
+using Microsoft.AspNetCore.Mvc;
+using Microsoft.AspNetCore.Mvc.Filters;
+using Microsoft.Extensions.DependencyInjection;
+
+namespace PluralKit.API
+{
+    public class RequiresSystemAttribute: ActionFilterAttribute
+    {
+
+        public override async Task OnActionExecutionAsync(ActionExecutingContext context, ActionExecutionDelegate next)
+        {
+            var auth = context.HttpContext.RequestServices.GetRequiredService<TokenAuthService>();
+            if (auth.CurrentSystem == null)
+            {
+                context.Result = new UnauthorizedObjectResult("Invalid or missing token in Authorization header.");
+                return;
+            }
+
+            await base.OnActionExecutionAsync(context, next);
+        }
+    }
+}