Switch over to a check-based system with multi attribute support

SimpleHttpServer/Types/BaseEndpointCheckAttribute.cs

@@ -0,0 +1,15 @@
+using System.Net;
+
+namespace SimpleHttpServer.Types;
+
+[AttributeUsage(AttributeTargets.Method | AttributeTargets.Class, Inherited = true, AllowMultiple = true)]
+public abstract class BaseEndpointCheckAttribute : Attribute {
+
+    public BaseEndpointCheckAttribute() { }
+
+    /// <summary>
+    /// Executed when the endpoint is invoked. The endpoint invocation is skipped if any of the checks fail.
+    /// </summary>
+    /// <returns>True to allow invocation, false to prevent.</returns>
+    public abstract bool Check(HttpListenerRequest req);
+}