Add caching_sha2_password auth response unit and integration coverage

src/SuperSocket.MySQL/MySQLConnection.cs

@@ -199,7 +199,7 @@ private byte[] GenerateNativePasswordResponse(byte[] salt)
             }
         }
 
-        private byte[] GenerateCachingSha2Response(byte[] salt)
+        internal byte[] GenerateCachingSha2Response(byte[] salt)
         {
             if (string.IsNullOrEmpty(_password))
                 return Array.Empty<byte>();
@@ -383,4 +383,4 @@ protected override void OnClosed(object sender, EventArgs e)
             base.OnClosed(sender, e);
         }
     }
-}
+}

tests/SuperSocket.MySQL.Test/HandshakeTest.cs

@@ -1,6 +1,7 @@
 using System;
 using System.Buffers;
 using System.Collections.Generic;
+using System.Security.Cryptography;
 using System.Text;
 using System.Threading.Tasks;
 using Xunit;
@@ -202,6 +203,40 @@ public void MySQLConnection_GenerateAuthResponse_ShouldHandleDifferentPasswords(
             Assert.NotNull(connection);
         }
 
+        [Fact]
+        public void MySQLConnection_GenerateCachingSha2Response_ShouldMatchExpected()
+        {
+            // Arrange
+            const string password = "test_password";
+            var connection = new MySQLConnection("localhost", 3306, "user", password);
+            // Include a trailing null byte to validate trimming of the salt.
+            var salt = new byte[] { 0x33, 0x21, 0x55, 0x42, 0x19, 0x76, 0xA1, 0x0B, 0x10, 0x5C, 0x2D, 0x48, 0x5A, 0x00 };
+
+            // Act
+            var response = connection.GenerateCachingSha2Response(salt);
+
+            // Assert
+            var trimmedSaltLength = salt[^1] == 0 ? salt.Length - 1 : salt.Length;
+            var trimmedSalt = new byte[trimmedSaltLength];
+            Array.Copy(salt, trimmedSalt, trimmedSaltLength);
+
+            using var sha256 = SHA256.Create();
+            var passwordBytes = Encoding.UTF8.GetBytes(password);
+            var sha256Password = sha256.ComputeHash(passwordBytes);
+            var sha256Sha256Password = sha256.ComputeHash(sha256Password);
+            var hashAndSalt = new byte[sha256Sha256Password.Length + trimmedSalt.Length];
+            Array.Copy(sha256Sha256Password, 0, hashAndSalt, 0, sha256Sha256Password.Length);
+            Array.Copy(trimmedSalt, 0, hashAndSalt, sha256Sha256Password.Length, trimmedSalt.Length);
+            var sha256Combined = sha256.ComputeHash(hashAndSalt);
+            var expected = new byte[sha256Password.Length];
+            for (int i = 0; i < expected.Length; i++)
+            {
+                expected[i] = (byte)(sha256Password[i] ^ sha256Combined[i]);
+            }
+
+            Assert.Equal(expected, response);
+        }
+
         [Fact]
         public void EOFPacket_ShouldNotIndicateAuthenticationSuccess()
         {