Baustein 1: Server-Auth-Fix (Kapitel 10)

/api/auth/login und /api/auth/register akzeptierten zuvor jeden
beliebigen Nutzernamen/Passwort und stellten ein gueltiges 30-Tage-JWT
aus - konkrete, ausnutzbare Luecke bei echtem Deployment.

- PasswordHasher (PBKDF2, Salt pro Nutzer) + UserStore (LiteDB) statt
  des ungeprueften Stubs
- /api/auth/register ersatzlos entfernt (kein offener
  Registrierungs-Endpunkt fuer ein Einzel-/Familien-Deployment)
- Neue Nutzer per CLI (dotnet LehrerApp.Api.dll create-user <name>),
  dokumentiert in docker/README.md
- Neues Testprojekt LehrerApp.Api.Tests (bisher als einziges Projekt
  ohne Tests)

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

LehrerApp.Api/Cli.cs

@@ -0,0 +1,56 @@
+using System.Text;
+
+namespace LehrerApp.Api;
+
+internal static class Cli
+{
+    public static Task<int> RunCreateUserAsync(string dataPath, string[] args)
+    {
+        if (args.Length < 2)
+        {
+            Console.Error.WriteLine("Verwendung: create-user <benutzername> [--password <passwort>]");
+            return Task.FromResult(1);
+        }
+
+        var username = args[1];
+        string? password = null;
+        for (var i = 2; i < args.Length - 1; i++)
+            if (args[i] == "--password") password = args[i + 1];
+
+        password ??= ReadPassword("Passwort (mind. 12 Zeichen): ");
+
+        if (string.IsNullOrWhiteSpace(password) || password.Length < 12)
+        {
+            Console.Error.WriteLine("Passwort muss mindestens 12 Zeichen lang sein.");
+            return Task.FromResult(1);
+        }
+
+        Directory.CreateDirectory(dataPath);
+        using var store = new UserStore(dataPath);
+        if (!store.CreateUser(username, password))
+        {
+            Console.Error.WriteLine($"Nutzer '{username}' existiert bereits.");
+            return Task.FromResult(1);
+        }
+
+        Console.WriteLine($"Nutzer '{username}' angelegt.");
+        return Task.FromResult(0);
+    }
+
+    // docker exec ohne -it liefert kein TTY -> ReadKey wäre nicht möglich, dann normal lesen.
+    private static string ReadPassword(string prompt)
+    {
+        Console.Write(prompt);
+        if (Console.IsInputRedirected) return Console.ReadLine() ?? "";
+
+        var sb = new StringBuilder();
+        ConsoleKeyInfo key;
+        while ((key = Console.ReadKey(intercept: true)).Key != ConsoleKey.Enter)
+        {
+            if (key.Key == ConsoleKey.Backspace && sb.Length > 0) { sb.Length--; Console.Write("\b \b"); }
+            else if (!char.IsControl(key.KeyChar)) { sb.Append(key.KeyChar); Console.Write('*'); }
+        }
+        Console.WriteLine();
+        return sb.ToString();
+    }
+}

LehrerApp.Api/Endpoints/Endpoints.cs

@@ -14,19 +14,12 @@ public static class Endpoints
 
     public static void MapAuthEndpoints(this WebApplication app, string secret)
     {
-        app.MapPost("/api/auth/login", (LoginRequest req) =>
+        app.MapPost("/api/auth/login", (LoginRequest req, UserStore store) =>
         {
             if (string.IsNullOrWhiteSpace(req.Username) || string.IsNullOrWhiteSpace(req.Password))
                 return Results.Unauthorized();
-            // TODO: Passwort gegen DB prüfen
-            return Results.Ok(new { token = Jwt(req.Username, secret), userId = req.Username });
-        });
-
-        app.MapPost("/api/auth/register", (RegisterRequest req) =>
-        {
-            if (req.Password.Length < 12)
-                return Results.BadRequest("Passwort mind. 12 Zeichen.");
-            // TODO: User anlegen, Passwort hashen (BCrypt)
+            if (!store.VerifyPassword(req.Username, req.Password))
+                return Results.Unauthorized();
             return Results.Ok(new { token = Jwt(req.Username, secret), userId = req.Username });
         });
     }
@@ -130,4 +123,3 @@ public static class Endpoints
 }
 
 public record LoginRequest(string Username, string Password);
-public record RegisterRequest(string Username, string Password, string DisplayName);

LehrerApp.Api/PasswordHasher.cs

@@ -0,0 +1,27 @@
+using System.Security.Cryptography;
+
+namespace LehrerApp.Api;
+
+public static class PasswordHasher
+{
+    private const int Iterations = 100_000;
+    private const int SaltSize = 16;
+    private const int HashSize = 32;
+
+    public static string Hash(string password)
+    {
+        var salt = RandomNumberGenerator.GetBytes(SaltSize);
+        var hash = Rfc2898DeriveBytes.Pbkdf2(password, salt, Iterations, HashAlgorithmName.SHA256, HashSize);
+        return $"{Convert.ToBase64String(salt)}:{Convert.ToBase64String(hash)}";
+    }
+
+    public static bool Verify(string password, string stored)
+    {
+        var parts = stored.Split(':');
+        if (parts.Length != 2) return false;
+        var salt = Convert.FromBase64String(parts[0]);
+        var expected = Convert.FromBase64String(parts[1]);
+        var actual = Rfc2898DeriveBytes.Pbkdf2(password, salt, Iterations, HashAlgorithmName.SHA256, HashSize);
+        return CryptographicOperations.FixedTimeEquals(actual, expected);
+    }
+}

LehrerApp.Api/Program.cs

@@ -11,6 +11,11 @@ builder.WebHost.UseKestrel(o =>
     o.ListenAnyIP(port);
 });
 
+var data = builder.Configuration["Api:DataPath"] ?? "./data";
+
+if (args.Length > 0 && args[0] == "create-user")
+    return await Cli.RunCreateUserAsync(data, args);
+
 var secret = builder.Configuration["JWT_SECRET"]
     ?? throw new InvalidOperationException("JWT_SECRET nicht konfiguriert.");
 
@@ -24,7 +29,7 @@ builder.Services.AddAuthentication(JwtBearerDefaults.AuthenticationScheme)
     });
 builder.Services.AddAuthorization();
 
-var data = builder.Configuration["Api:DataPath"] ?? "./data";
+builder.Services.AddSingleton<UserStore>(_ => new UserStore(data));
 builder.Services.AddSingleton<EventStore>(_ => new EventStore(data));
 builder.Services.AddSingleton<SnapshotStore>(_ => new SnapshotStore(data));
 builder.Services.AddSingleton<ReadableSnapshotStore>(_ => new ReadableSnapshotStore(data));
@@ -40,3 +45,4 @@ app.MapSnapshotEndpoints();
 app.MapReadableSnapshotEndpoints();
 app.MapPlainSyncEndpoints();
 app.Run();
+return 0;

LehrerApp.Api/UserStore.cs

@@ -0,0 +1,40 @@
+using LiteDB;
+
+namespace LehrerApp.Api;
+
+public class UserStore(string dataPath) : IDisposable
+{
+    private readonly LiteDatabase _db = new(Path.Combine(dataPath, "users.db"));
+
+    private ILiteCollection<UserEntry> Col
+    {
+        get
+        {
+            var col = _db.GetCollection<UserEntry>("users");
+            col.EnsureIndex(x => x.Username, unique: true);
+            return col;
+        }
+    }
+
+    public bool CreateUser(string username, string password)
+    {
+        if (Col.Exists(x => x.Username == username)) return false;
+        Col.Insert(new UserEntry { Username = username, PasswordHash = PasswordHasher.Hash(password) });
+        return true;
+    }
+
+    public bool VerifyPassword(string username, string password)
+    {
+        var user = Col.FindOne(x => x.Username == username);
+        return user is not null && PasswordHasher.Verify(password, user.PasswordHash);
+    }
+
+    public void Dispose() => _db.Dispose();
+}
+
+internal class UserEntry
+{
+    public ObjectId Id { get; set; } = ObjectId.NewObjectId();
+    public string Username { get; set; } = "";
+    public string PasswordHash { get; set; } = "";
+}