Add auth service

Service/Service.Core/Services/PasswordHasher.cs

@@ -0,0 +1,56 @@
+using System.Security.Cryptography;
+using System.Text;
+using Konscious.Security.Cryptography;
+
+namespace BusinessLayer.Services
+{
+    public static class PasswordHasher
+    {
+        private const int SaltSize = 16; // 128-bit
+        private const int HashSize = 32; // 256-bit
+        private const int ArgonIterations = 4;
+        private const int ArgonMemoryKb = 65536; // 64MB
+
+        public static string Hash(string password)
+        {
+            var salt = RandomNumberGenerator.GetBytes(SaltSize);
+            var argon2 = new Argon2id(Encoding.UTF8.GetBytes(password))
+            {
+                Salt = salt,
+                DegreeOfParallelism = Math.Max(Environment.ProcessorCount, 1),
+                MemorySize = ArgonMemoryKb,
+                Iterations = ArgonIterations
+            };
+
+            var hash = argon2.GetBytes(HashSize);
+            return $"{Convert.ToBase64String(salt)}:{Convert.ToBase64String(hash)}";
+        }
+
+        public static bool Verify(string password, string stored)
+        {
+            try
+            {
+                var parts = stored.Split(':', StringSplitOptions.RemoveEmptyEntries);
+                if (parts.Length != 2) return false;
+
+                var salt = Convert.FromBase64String(parts[0]);
+                var expected = Convert.FromBase64String(parts[1]);
+
+                var argon2 = new Argon2id(Encoding.UTF8.GetBytes(password))
+                {
+                    Salt = salt,
+                    DegreeOfParallelism = Math.Max(Environment.ProcessorCount, 1),
+                    MemorySize = ArgonMemoryKb,
+                    Iterations = ArgonIterations
+                };
+
+                var actual = argon2.GetBytes(expected.Length);
+                return CryptographicOperations.FixedTimeEquals(actual, expected);
+            }
+            catch
+            {
+                return false;
+            }
+        }
+    }
+}