Initial commit: BARON SSO 샘플 (WebView OIDC PKCE 인증 라이브러리 + 데모 앱)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

BaronSoftware.SSO/Exceptions/InvalidUserException.cs

@@ -0,0 +1,15 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace BaronSoftware.SSO.Exceptions
+{
+    internal class InvalidUserException : Exception
+    {   
+        public InvalidUserException() { }
+        public InvalidUserException(string message) : base(message) { }
+        public InvalidUserException(string message, Exception inner) : base(message, inner) { }
+    }
+}