hopefully not a horribly foolish refactoring

Femto.Modules.Authentication/Models/Events/UserWasCreatedEvent.cs

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+using Femto.Common.Domain;
+
+namespace Femto.Modules.Authentication.Models.Events;
+
+internal record UserWasCreatedEvent(UserIdentity User) : DomainEvent;

Femto.Modules.Authentication/Models/UserIdentity.cs

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+using System.Text;
+using Femto.Common.Domain;
+using Femto.Modules.Authentication.Contracts;
+using Femto.Modules.Authentication.Models.Events;
+using Geralt;
+
+namespace Femto.Modules.Authentication.Models;
+
+internal class UserIdentity : Entity
+{
+    public Guid Id { get; private set; }
+    
+    public string Username { get; private set; }
+    
+    public UserPassword Password { get; private set; }
+
+    private UserIdentity()
+    {
+        
+    }
+
+    public UserIdentity(string username)
+    {
+        this.Id = Guid.CreateVersion7();
+        this.Username = username;
+        
+        this.AddDomainEvent(new UserWasCreatedEvent(this));
+    }
+
+    public UserIdentity WithPassword(string password)
+    {
+        this.SetPassword(password);
+        return this;
+    }
+
+    public void SetPassword(string password)
+    {
+        var hash = new byte[128];
+        try
+        {
+            Argon2id.ComputeHash(hash, Encoding.UTF8.GetBytes(password), 3, 67108864);
+        }
+        catch (Exception e)
+        {
+            throw new SetPasswordError("Failed to hash password", e);
+        }
+        
+        this.Password = new UserPassword(this.Id, hash, new byte[128]);
+    }
+}
+
+public class SetPasswordError(string message, Exception inner) : DomainException(message, inner);

Femto.Modules.Authentication/Models/UserPassword.cs

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+namespace Femto.Modules.Authentication.Models;
+
+internal class UserPassword
+{
+    public Guid Id { get; private set; }
+    
+    public byte[] Hash { get; private set; }
+    
+    public byte[] Salt { get; private set; }
+    
+    private UserPassword() {}
+    
+    public UserPassword(Guid id, byte[] hash, byte[] salt)
+    {
+        Id = id;
+        Hash = hash;
+        Salt = salt;
+    }
+}