diff --git a/Common/NtlmHelper.cs b/Common/NtlmHelper.cs
new file mode 100644
index 0000000..9372034
--- /dev/null
+++ b/Common/NtlmHelper.cs
@@ -0,0 +1,33 @@
+using Microsoft.Win32.SafeHandles;
+using System.Runtime.InteropServices;
+
+namespace FakeNTLMServer.Common
+{
+    public static class NtlmHelper
+    {
+        [DllImport("advapi32.dll", SetLastError = true, CharSet = CharSet.Unicode)]
+        private static extern bool LogonUser(
+            string lpszUsername,
+            string lpszDomain,
+            string lpszPassword,
+            int dwLogonType,
+            int dwLogonProvider,
+            out SafeAccessTokenHandle phToken);
+
+        private const int LOGON32_LOGON_NETWORK = 3;
+        private const int LOGON32_PROVIDER_DEFAULT = 0;
+
+        public static bool ValidateCredentials(string username, string domain, string password, out SafeAccessTokenHandle token)
+        {
+            var success = LogonUser(
+                username,
+                domain,
+                password,
+                LOGON32_LOGON_NETWORK,
+                LOGON32_PROVIDER_DEFAULT,
+                out token);
+
+            return success && token is not null && !token.IsInvalid;
+        }
+    }
+}