Reworked encryption to use less heap allocated buffers for secrets.

Also some work on plugin system.

IdentityShroud.Core/Plugins/PluginLoader.cs

@@ -0,0 +1,59 @@
+using System.Reflection;
+using System.Runtime.Loader;
+using IdentityShroud.PluginSupport;
+
+namespace IdentityShroud.Core.Plugins;
+
+public static class PluginLoader
+{
+    public static IEnumerable<IPlugin> LoadPlugins(string pluginsFolder)
+    {
+        if (!Directory.Exists(pluginsFolder))
+            yield break;
+
+        foreach (var dll in Directory.EnumerateFiles(pluginsFolder, "*.dll"))
+        {
+            foreach (var plugin in LoadPluginDll(dll)) yield return plugin;
+        }
+    }
+
+    private static IEnumerable<IPlugin> LoadPluginDll(string dll)
+    {
+        Assembly asm;
+        try
+        {
+            asm = AssemblyLoadContext.Default.LoadFromAssemblyPath(Path.GetFullPath(dll));
+        }
+        catch
+        {
+            yield break;
+        }
+
+        IEnumerable<Type> pluginTypes;
+        try
+        {
+            pluginTypes = asm.GetTypes()
+                .Where(t => typeof(IPlugin).IsAssignableFrom(t) && t is { IsInterface: false, IsAbstract: false });
+        }
+        catch
+        {
+            yield break;
+        }
+
+        foreach (var t in pluginTypes)
+        {
+            IPlugin? instance = null;
+            try
+            {
+                instance = (IPlugin?)Activator.CreateInstance(t);
+            }
+            catch
+            {
+                // ignore bad plugin types
+            }
+
+            if (instance != null)
+                yield return instance;
+        }
+    }
+}