fix(auth): an account with a password deletes itself only with it and a code

A session alone deleted any account, with everything encrypted under its
keys (the second reading's lows; decided by the developer: the password
and a code, as a change of password takes). account.delete now takes a
DeletionProof (the password's SRP proof for a beginChange challenge, a
TOTP or recovery code, the host the device addressed); the register
checks it (requireOwnerToDelete), a member passing it on bound to its own
host. Accounts without a password, anonymous ones among them, delete with
their session as before. In the app, deleting an account with a password
asks for it and a code in a sheet of its own; a wrong one deletes
nothing.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Tizian 「ティツィアーン」 <raisondetredev@pm.me>

packages/halkyon_app/lib/l10n/halkyon_app_de.arb

@@ -209,5 +209,6 @@
   "passwordFailed": "Die Instanz war nicht erreichbar. Prüf die Verbindung und versuch es noch einmal.",
   "passwordMinLength": "Mindestens {count} Zeichen",
   "passwordTooShort": "Ein neues Passwort braucht mindestens {count} Zeichen: Sollte die Datenbank der Instanz je nach außen gelangen, wird ein kurzes zuerst erraten.",
-  "passwordCodesWait": "Zu viele falsche Codes hintereinander: Bis {date} wird kein Code angenommen. Waren es nicht deine, kennt jemand dein Passwort: Ändere es dann."
+  "passwordCodesWait": "Zu viele falsche Codes hintereinander: Bis {date} wird kein Code angenommen. Waren es nicht deine, kennt jemand dein Passwort: Ändere es dann.",
+  "passwordDeleteIntro": "Dein Konto wird mit allem darin gelöscht, in jedem Dienst dieser Instanz. Gib zur Bestätigung dein Passwort und einen Code deiner Authenticator-App ein."
 }

packages/halkyon_app/lib/l10n/halkyon_app_en.arb

@@ -456,5 +456,6 @@
         "type": "String"
       }
     }
-  }
+  },
+  "passwordDeleteIntro": "Your account goes with everything in it, in every service of this instance. To confirm, type your password and a code from your authenticator app."
 }

packages/halkyon_app/lib/l10n/halkyon_app_localizations.dart

@@ -1362,6 +1362,12 @@ abstract class HalkyonAppLocalizations {
   /// In en, this message translates to:
   /// **'Too many wrong codes in a row: no code is taken until {date}. If they weren\'t yours, someone knows your password: change it then.'**
   String passwordCodesWait(String date);
+
+  /// No description provided for @passwordDeleteIntro.
+  ///
+  /// In en, this message translates to:
+  /// **'Your account goes with everything in it, in every service of this instance. To confirm, type your password and a code from your authenticator app.'**
+  String get passwordDeleteIntro;
 }
 
 class _HalkyonAppLocalizationsDelegate

packages/halkyon_app/lib/l10n/halkyon_app_localizations_de.dart

@@ -788,4 +788,8 @@ class HalkyonAppLocalizationsDe extends HalkyonAppLocalizations {
   String passwordCodesWait(String date) {
     return 'Zu viele falsche Codes hintereinander: Bis $date wird kein Code angenommen. Waren es nicht deine, kennt jemand dein Passwort: Ändere es dann.';
   }
+
+  @override
+  String get passwordDeleteIntro =>
+      'Dein Konto wird mit allem darin gelöscht, in jedem Dienst dieser Instanz. Gib zur Bestätigung dein Passwort und einen Code deiner Authenticator-App ein.';
 }

packages/halkyon_app/lib/l10n/halkyon_app_localizations_en.dart

@@ -771,6 +771,10 @@ class HalkyonAppLocalizationsEn extends HalkyonAppLocalizations {
   String passwordCodesWait(String date) {
     return 'Too many wrong codes in a row: no code is taken until $date. If they weren\'t yours, someone knows your password: change it then.';
   }
+
+  @override
+  String get passwordDeleteIntro =>
+      'Your account goes with everything in it, in every service of this instance. To confirm, type your password and a code from your authenticator app.';
 }
 
 /// The translations for English, as used in the United Kingdom (`en_GB`).

packages/halkyon_app/lib/src/auth/widget/account_tiles.dart

@@ -4,6 +4,8 @@ import 'package:halkyon_app/src/app/app_scope.dart';
 import 'package:halkyon_app/src/auth/bloc/session_bloc.dart';
 import 'package:halkyon_app/src/instance/instance_scope.dart';
 import 'package:halkyon_app/src/instance/widget/account_switcher_sheet.dart';
+import 'package:halkyon_app/src/password/model/password_failed.dart';
+import 'package:halkyon_app/src/password/widget/delete_account_sheet.dart';
 import 'package:halkyon_ui/halkyon_ui.dart';
 import 'package:lucide_icons_flutter/lucide_icons.dart';
 import 'package:material_ui/material_ui.dart';
@@ -104,17 +106,37 @@ class const AccountTiles({
     session.add(const SessionEventSignOutRequested());
   }
 
-  /// Deletes the account with everything in it, after asking.
+  /// Deletes the account with everything in it, after asking; an account
+  /// with a password only with it and a code (ADR 0017), which a sheet asks
+  /// for.
   Future<void> _delete(BuildContext context) async {
     final l10n = HalkyonAppLocalizations.of(context);
     final session = context.read<SessionBloc>();
-    if (await confirmDestructiveAction(
+    final passwords = AppScope.of(context).passwords;
+    final identified = switch (session.state) {
+      SessionStateActive(:final person) => person.isIdentified,
+      _ => false,
+    };
+    if (!await confirmDestructiveAction(
       context,
       title: l10n.accountDeleteTitle,
       message: deleteMessage,
       confirmLabel: l10n.accountDelete,
     )) {
+      return;
+    }
+    final bool hasPassword;
+    try {
+      hasPassword = identified && (await passwords.security()).hasPassword;
+    } on PasswordFailed {
+      // Unreachable: deleting would fail too, as the session bloc says.
       session.add(const SessionEventDeleteRequested());
+      return;
+    }
+    if (!hasPassword) {
+      session.add(const SessionEventDeleteRequested());
+    } else if (context.mounted) {
+      await showDeleteAccountWithPassword(context);
     }
   }
 }

packages/halkyon_app/lib/src/password/data/password_gateway.dart

@@ -105,6 +105,16 @@ abstract interface class PasswordGateway() {
   /// A change of password's first step.
   Future<protocol.PasswordChallenge> beginChange();
 
+  /// Deletes the signed-in person's account, which has a password: [answer]
+  /// to [challenge] ([beginChange]) proves it, with a [totpCode] or
+  /// [recoveryCode]; this device then forgets its session.
+  Future<void> deleteAccount(
+    protocol.PasswordChallenge challenge,
+    SrpAnswer answer, {
+    String? totpCode,
+    String? recoveryCode,
+  });
+
   /// Changes the password: [answer] to [challenge] proves the old one.
   Future<void> change(
     protocol.PasswordChallenge challenge,

packages/halkyon_app/lib/src/password/data/password_repository.dart

@@ -344,6 +344,29 @@ class PasswordRepository(
     _changed();
   }
 
+  /// Deletes the signed-in person's account, which has a password, with
+  /// [password] and a [totpCode] or [recoveryCode], as a change of password
+  /// takes (a session alone deletes only an account without one): on the
+  /// instance and every service of it, then signed out here.
+  Future<void> deleteAccount({
+    required String password,
+    String? totpCode,
+    String? recoveryCode,
+  }) async {
+    final challenge = await _gateway.beginChange();
+    final unlock = await _crypto.unlock(
+      password,
+      salt: Uint8List.sublistView(challenge.salt),
+      costs: challenge.costs,
+    );
+    await _gateway.deleteAccount(
+      challenge,
+      await _crypto.answer(unlock, challenge, host: _gateway.host),
+      totpCode: totpCode?.replaceAll(' ', ''),
+      recoveryCode: recoveryCode,
+    );
+  }
+
   /// A new recovery phrase for the signed-in person's keys, to show; the
   /// instance takes it with [keepPhrase].
   Future<NewPhrase> newPhrase() async {

packages/halkyon_app/lib/src/password/data/serverpod_password_gateway.dart

@@ -179,6 +179,28 @@ class ServerpodPasswordGateway(
   Future<protocol.PasswordChallenge> beginChange() =>
       _failing(_base.password.beginChange);
 
+  @override
+  Future<void> deleteAccount(
+    protocol.PasswordChallenge challenge,
+    SrpAnswer answer, {
+    String? totpCode,
+    String? recoveryCode,
+  }) => _failing(() async {
+    await _base.account.delete(
+      proof: protocol.DeletionProof(
+        challenge: challenge.challenge,
+        clientValue: answer.clientValue,
+        clientProof: answer.clientProof,
+        totpCode: totpCode,
+        recoveryCode: recoveryCode,
+        host: host,
+      ),
+    );
+    // The server ended every session of the person; forget this device's
+    // copy, which signs out here too.
+    await _client.auth.updateSignedInUser(null);
+  });
+
   @override
   Future<void> change(
     protocol.PasswordChallenge challenge,

packages/halkyon_app/lib/src/password/widget/delete_account_sheet.dart

@@ -0,0 +1,95 @@
+import 'package:flutter_bloc/flutter_bloc.dart';
+import 'package:halkyon_app/l10n/halkyon_app_localizations.dart';
+import 'package:halkyon_app/src/app/app_scope.dart';
+import 'package:halkyon_app/src/password/bloc/account_security_cubit.dart';
+import 'package:halkyon_app/src/password/widget/password_texts.dart';
+import 'package:halkyon_app/src/password/widget/password_widgets.dart';
+import 'package:halkyon_ui/halkyon_ui.dart';
+import 'package:material_ui/material_ui.dart';
+
+/// Deletes the signed-in person's account, which has a password: the
+/// password and a code from an authenticator, as changing the password
+/// takes (ADR 0017; the second reading). Once deleted, the person is signed
+/// out here, and the app asks how to start.
+Future<void> showDeleteAccountWithPassword(BuildContext context) =>
+    showAdaptiveSheet<void>(
+      context,
+      swipeable: false,
+      builder: (context) => const _DeleteAccount(),
+    );
+
+class const _DeleteAccount() extends StatefulWidget {
+  @override
+  State<_DeleteAccount> createState() => _DeleteAccountState();
+}
+
+class _DeleteAccountState() extends State<_DeleteAccount> {
+  final _password = TextEditingController();
+  final _code = TextEditingController();
+  late final _step = SecurityStepCubit<bool>();
+
+  @override
+  void dispose() {
+    _password.dispose();
+    _code.dispose();
+    _step.close();
+    super.dispose();
+  }
+
+  Future<void> _submit() async {
+    final passwords = AppScope.of(context).passwords;
+    await _step.run(() async {
+      await passwords.deleteAccount(
+        password: _password.text,
+        totpCode: _code.text,
+      );
+      return true;
+    });
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    final l10n = HalkyonAppLocalizations.of(context);
+    final colors = Theme.of(context).colorScheme;
+    return BlocBuilder<SecurityStepCubit<bool>, SecurityStepState<bool>>(
+      bloc: _step,
+      builder: (context, state) => SheetScaffold(
+        title: l10n.accountDeleteTitle,
+        busy: state.busy,
+        body: AutofillGroup(
+          child: state.busy
+              ? const SheetWorking()
+              : Column(
+                  crossAxisAlignment: CrossAxisAlignment.stretch,
+                  children: [
+                    SheetIntro(l10n.passwordDeleteIntro),
+                    PasswordField(
+                      controller: _password,
+                      label: l10n.passwordCurrent,
+                      autofocus: true,
+                    ),
+                    const SizedBox(height: 8),
+                    CodeField(
+                      controller: _code,
+                      kind: CodeKind.totp,
+                      errorText: switch (state.problem) {
+                        final failed? => passwordProblemText(context, failed),
+                        null => null,
+                      },
+                      onSubmitted: (_) => _submit(),
+                    ),
+                  ],
+                ),
+        ),
+        footer: FilledButton(
+          style: FilledButton.styleFrom(
+            backgroundColor: colors.error,
+            foregroundColor: colors.onError,
+          ),
+          onPressed: state.busy ? null : _submit,
+          child: Text(l10n.accountDelete),
+        ),
+      ),
+    );
+  }
+}

packages/halkyon_app/lib/src/testing/fake_password_gateway.dart

@@ -512,6 +512,21 @@ class FakePasswordGateway(final AuthGateway _auth) implements PasswordGateway {
     return _challengeFor(account.address);
   });
 
+  @override
+  Future<void> deleteAccount(
+    protocol.PasswordChallenge challenge,
+    SrpAnswer answer, {
+    String? totpCode,
+    String? recoveryCode,
+  }) async {
+    final account = await _call(
+      'deleteAccount',
+      () => _ownerProved(challenge, answer, totpCode, recoveryCode),
+    );
+    accounts.remove(account.address);
+    await _auth.deleteAccount();
+  }
+
   @override
   Future<void> change(
     protocol.PasswordChallenge challenge,