feat: added authentification and redirection

lib/data/repositories/auth_repository.dart

@@ -0,0 +1,43 @@
+import 'package:flutter/foundation.dart';
+import 'package:seshat/data/services/auth_client.dart';
+import 'package:seshat/utils/result.dart';
+
+class AuthRepository extends ChangeNotifier {
+  AuthRepository({required AuthClient authClient}) : _authClient = authClient;
+
+  final AuthClient _authClient;
+
+  bool? _isAuthenticated;
+
+  Future<bool> get isLoggedIn async {
+    if (_isAuthenticated != null) {
+      return _isAuthenticated!;
+    }
+    final result = await _authClient.hasValidToken();
+    switch (result) {
+      case Ok():
+        if (result.value) {
+          return true;
+        }
+        return false;
+      case Error():
+        return false;
+    }
+  }
+
+  Future<Result<void>> login(String username, String password) async {
+    try {
+      final result = await _authClient.login(username, password);
+      switch (result) {
+        case Ok():
+          _isAuthenticated = true;
+          return Result.ok(());
+        case Error():
+          return Result.error(result.error);
+      }
+    } catch (e, stackTrace) {
+      debugPrintStack(stackTrace: stackTrace);
+      return Result.error(Exception(e));
+    }
+  }
+}