Add encryption for Kaigen server auth

src/Managing.Application.Tests/CryptoHelpersTests.cs

@@ -0,0 +1,39 @@
+using System.Security.Cryptography;
+using Managing.Core;
+using Xunit;
+
+namespace Managing.Application.Tests;
+
+public class CryptoHelpersTests
+{
+    [Fact]
+    public void EncryptAesGcm_And_DecryptAesGcm_RoundTrip_Works()
+    {
+        // Arrange
+        var secretKey = "supersecretkey1234567890123456"; // 32 bytes
+        var token = "0x1234567890abcdef-johndoe";
+
+        // Act
+        var encrypted = CryptoHelpers.EncryptAesGcm(token, secretKey);
+        var decrypted = CryptoHelpers.DecryptAesGcm(encrypted, secretKey);
+
+        // Assert
+        Assert.NotNull(encrypted);
+        Assert.NotEqual(token, encrypted); // Should be encrypted
+        Assert.Equal(token, decrypted); // Should decrypt to original
+    }
+
+    [Fact]
+    public void DecryptAesGcm_WithWrongKey_Throws()
+    {
+        // Arrange
+        var secretKey = "supersecretkey1234567890123456";
+        var wrongKey = "wrongsecretkey6543210987654321";
+        var token = "0xabcdef-jane";
+        var encrypted = CryptoHelpers.EncryptAesGcm(token, secretKey);
+
+        // Act & Assert
+        Assert.Throws<CryptographicException>(() =>
+            CryptoHelpers.DecryptAesGcm(encrypted, wrongKey));
+    }
+}