Add username/password auth and login UI

Infrastructure/PasswordHasher.cs

@@ -0,0 +1,38 @@
+using System.Security.Cryptography;
+using System.Text;
+
+namespace GameList.Infrastructure;
+
+public static class PasswordHasher
+{
+    private const int SaltSize = 16;
+    private const int KeySize = 32;
+    private const int Iterations = 100_000;
+
+    public static (byte[] Hash, byte[] Salt) HashPassword(string password)
+    {
+        if (string.IsNullOrEmpty(password))
+            throw new ArgumentException("Password required", nameof(password));
+
+        var salt = RandomNumberGenerator.GetBytes(SaltSize);
+        var hash = PBKDF2(password, salt);
+        return (hash, salt);
+    }
+
+    public static bool Verify(string password, byte[] hash, byte[] salt)
+    {
+        if (hash is null || salt is null || hash.Length == 0 || salt.Length == 0) return false;
+        var computed = PBKDF2(password, salt);
+        return CryptographicOperations.FixedTimeEquals(computed, hash);
+    }
+
+    private static byte[] PBKDF2(string password, byte[] salt)
+    {
+        return Rfc2898DeriveBytes.Pbkdf2(
+            Encoding.UTF8.GetBytes(password),
+            salt,
+            Iterations,
+            HashAlgorithmName.SHA256,
+            KeySize);
+    }
+}