feat(caldav): app-specific passwords so MFA accounts can use CalDAV

CalDAV clients send only user+password over Basic Auth and can't provide a TOTP
code, so account passwords would bypass 2FA. Add revocable app passwords:

- models: AppPassword table (bcrypt hash, label, last_used); auto-created via
  create_all
- profile_router: GET/POST/DELETE /profile/app-passwords (plaintext shown once)
- dav_router: Basic Auth accepts any app password; the account password is
  accepted only when 2FA is disabled
- frontend: "App-Passwörter (CalDAV)" section in the profile modal (create/show-
  once/copy/revoke) + i18n (de/en); login hint now says app password

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

backend/models.py

@@ -114,6 +114,26 @@ class UserSettings(Base):
     user = relationship("User", back_populates="settings")
 
 
+class AppPassword(Base):
+    """Per-device app-specific password for CalDAV (Basic Auth).
+
+    Keeps MFA intact: accounts with 2FA can't use their normal password over
+    CalDAV (clients can't send a TOTP code), so they authenticate with one of
+    these revocable app passwords instead. Only the bcrypt hash is stored.
+    """
+
+    __tablename__ = "app_passwords"
+
+    id = Column(Integer, primary_key=True, index=True)
+    user_id = Column(Integer, ForeignKey("users.id"), nullable=False)
+    label = Column(String(100), nullable=False)
+    password_hash = Column(String(255), nullable=False)
+    created_at = Column(String(50), nullable=True)
+    last_used_at = Column(String(50), nullable=True)
+
+    user = relationship("User")
+
+
 class LocalCalendar(Base):
     __tablename__ = "local_calendars"
 

backend/routers/dav_router.py

@@ -21,6 +21,7 @@ from __future__ import annotations
 import base64
 import uuid
 import xml.etree.ElementTree as ET
+from datetime import datetime, timezone
 from urllib.parse import quote, unquote
 from xml.sax.saxutils import escape as xml_escape
 
@@ -70,7 +71,12 @@ def _resolve(token: str, db: Session) -> models.LocalCalendar | None:
 
 
 def _basic_auth_user(request: Request, db: Session) -> models.User | None:
-    """Validate an HTTP Basic Authorization header against a Calendarr account."""
+    """Validate an HTTP Basic Authorization header against a Calendarr account.
+
+    Accepts an app-specific password (always) or the account password (only when
+    MFA is off — otherwise the account password would bypass 2FA, which CalDAV
+    clients can't satisfy).
+    """
     hdr = request.headers.get("Authorization", "")
     if not hdr.lower().startswith("basic "):
         return None
@@ -84,12 +90,25 @@ def _basic_auth_user(request: Request, db: Session) -> models.User | None:
     user = db.query(models.User).filter(models.User.username == username).first()
     if not user:
         return None
-    try:
+
-        if not verify_password(password, user.password_hash):
+    # 1) App-specific passwords — always allowed, MFA-safe.
+    for ap in db.query(models.AppPassword).filter(models.AppPassword.user_id == user.id).all():
+        try:
+            if verify_password(password, ap.password_hash):
+                ap.last_used_at = datetime.now(timezone.utc).isoformat()
+                db.commit()
+                return user
+        except Exception:
+            continue
+
+    # 2) Account password — only when 2FA is disabled.
+    if not user.totp_enabled:
+        try:
+            if verify_password(password, user.password_hash):
+                return user
+        except Exception:
             return None
-    except Exception:
+    return None
-        return None
-    return user
 
 
 def _unauthorized() -> Response:

backend/routers/profile_router.py

@@ -1,6 +1,8 @@
 import io
 import re
 import base64
+import secrets
+from datetime import datetime, timezone
 from pathlib import Path
 from typing import Optional
 
@@ -264,3 +266,74 @@ def disable_totp(
     current_user.totp_enabled = False
     db.commit()
     return {"ok": True}
+
+
+# ── App passwords (for CalDAV Basic Auth) ────────────────
+class AppPasswordCreate(BaseModel):
+    label: str = Field(default="CalDAV", max_length=100)
+
+
+def _app_pw_dict(ap: models.AppPassword) -> dict:
+    return {
+        "id": ap.id,
+        "label": ap.label,
+        "created_at": ap.created_at,
+        "last_used_at": ap.last_used_at,
+    }
+
+
+@router.get("/app-passwords")
+def list_app_passwords(
+    db: Session = Depends(get_db),
+    current_user: models.User = Depends(get_current_user),
+):
+    rows = (
+        db.query(models.AppPassword)
+        .filter(models.AppPassword.user_id == current_user.id)
+        .order_by(models.AppPassword.id.desc())
+        .all()
+    )
+    return [_app_pw_dict(r) for r in rows]
+
+
+@router.post("/app-passwords")
+def create_app_password(
+    data: AppPasswordCreate,
+    db: Session = Depends(get_db),
+    current_user: models.User = Depends(get_current_user),
+):
+    # Show the plaintext exactly once; only the hash is stored.
+    password = secrets.token_urlsafe(18)
+    ap = models.AppPassword(
+        user_id=current_user.id,
+        label=(data.label or "CalDAV")[:100],
+        password_hash=get_password_hash(password),
+        created_at=datetime.now(timezone.utc).isoformat(),
+    )
+    db.add(ap)
+    db.commit()
+    db.refresh(ap)
+    out = _app_pw_dict(ap)
+    out["password"] = password
+    return out
+
+
+@router.delete("/app-passwords/{ap_id}")
+def delete_app_password(
+    ap_id: int,
+    db: Session = Depends(get_db),
+    current_user: models.User = Depends(get_current_user),
+):
+    ap = (
+        db.query(models.AppPassword)
+        .filter(
+            models.AppPassword.id == ap_id,
+            models.AppPassword.user_id == current_user.id,
+        )
+        .first()
+    )
+    if not ap:
+        raise HTTPException(404, "App password not found")
+    db.delete(ap)
+    db.commit()
+    return {"ok": True}

frontend/css/app.css

@@ -1472,6 +1472,12 @@ a { color: var(--primary); text-decoration: none; }
   background: var(--surface-2); color: var(--text-1);
 }
 .ct-dav-hint { font-size: 11px; color: var(--text-3); margin-top: 6px; max-width: 640px; }
+.app-pw-create { display: flex; gap: 8px; align-items: center; }
+.app-pw-create input { flex: 1; }
+.app-pw-new { margin: 8px 0; }
+.app-pw-item { display: flex; align-items: center; gap: 10px; padding: 6px 0; border-top: 1px solid var(--border); }
+.app-pw-name { font-weight: 500; }
+.app-pw-meta { font-size: 11px; color: var(--text-3); margin-left: auto; }
 .ct-eye, .ct-bell { opacity: .45; transition: opacity .15s; }
 .ct-eye[data-ct-visible="1"], .ct-bell[data-ct-on="1"] { opacity: 1; }
 .ct-eye:hover, .ct-bell:hover { opacity: 1; }

frontend/index.html

@@ -995,6 +995,26 @@
         </div>
       </div>
 
+      <!-- App passwords (CalDAV) -->
+      <div class="settings-section">
+        <h4 data-i18n="app_pw_title">App-Passwörter (CalDAV)</h4>
+        <p class="text-muted" data-i18n="app_pw_desc">Eigene Passwörter für CalDAV-Clients. Bei aktivem 2FA nötig, da Apps keinen 2FA-Code eingeben können. Jederzeit widerrufbar.</p>
+        <div class="form-group app-pw-create">
+          <input type="text" id="app-pw-label" data-i18n-placeholder="app_pw_label_ph" placeholder="Name (z.B. iPhone)" maxlength="100" />
+          <button class="btn btn-primary btn-sm" id="app-pw-create-btn" data-i18n="app_pw_create">Erstellen</button>
+        </div>
+        <div id="app-pw-new" class="app-pw-new hidden">
+          <label data-i18n="app_pw_new_label">Neues App-Passwort (nur jetzt sichtbar):</label>
+          <div class="totp-secret-row">
+            <code id="app-pw-new-value"></code>
+            <button class="btn btn-ghost btn-sm" id="app-pw-copy" title="Kopieren">
+              <svg viewBox="0 0 24 24" fill="currentColor" width="16" height="16"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg>
+            </button>
+          </div>
+        </div>
+        <div id="app-pw-list"></div>
+      </div>
+
       <!-- Calendars -->
       <div class="settings-section">
         <h4>Meine Kalender</h4>

frontend/js/calendar.js

@@ -4144,6 +4144,50 @@ function bindProfileModal() {
       document.getElementById('2fa-disable-pw').value = '';
     } catch (e) { showToast(e.message, true); }
   };
+
+  // ── App passwords (CalDAV) ──
+  const appPwList = document.getElementById('app-pw-list');
+  document.getElementById('app-pw-new').classList.add('hidden');
+  document.getElementById('app-pw-new-value').textContent = '';
+  async function loadAppPasswords() {
+    try {
+      const rows = await api.get('/profile/app-passwords');
+      appPwList.innerHTML = rows.length
+        ? rows.map(r => `<div class="app-pw-item">
+            <span class="app-pw-name">${escHtml(r.label)}</span>
+            <span class="app-pw-meta">${r.last_used_at ? t('app_pw_last_used') + ' ' + new Date(r.last_used_at).toLocaleDateString() : t('app_pw_never_used')}</span>
+            <button class="btn btn-ghost btn-sm app-pw-del" data-id="${r.id}">${t('app_pw_revoke')}</button>
+          </div>`).join('')
+        : `<p class="text-muted">${t('app_pw_none')}</p>`;
+    } catch (e) { /* ignore */ }
+  }
+  loadAppPasswords();
+
+  document.getElementById('app-pw-create-btn').onclick = async () => {
+    const label = document.getElementById('app-pw-label').value.trim() || 'CalDAV';
+    try {
+      const res = await api.post('/profile/app-passwords', { label });
+      document.getElementById('app-pw-new-value').textContent = res.password;
+      document.getElementById('app-pw-new').classList.remove('hidden');
+      document.getElementById('app-pw-label').value = '';
+      loadAppPasswords();
+    } catch (e) { showToast(e.message, true); }
+  };
+
+  document.getElementById('app-pw-copy').onclick = () => {
+    const v = document.getElementById('app-pw-new-value').textContent;
+    if (v) navigator.clipboard.writeText(v).then(() => showToast(t('app_pw_copied')));
+  };
+
+  appPwList.onclick = async (e) => {
+    const btn = e.target.closest('.app-pw-del');
+    if (!btn) return;
+    if (!confirm(t('app_pw_revoke_confirm'))) return;
+    try {
+      await api.delete(`/profile/app-passwords/${btn.dataset.id}`);
+      loadAppPasswords();
+    } catch (err) { showToast(err.message, true); }
+  };
 }
 
 function updateTopbarAvatar(hasAvatar) {

frontend/js/i18n.js

@@ -124,7 +124,18 @@ const translations = {
     caldav_rotate_confirm: 'Neuen Token erzeugen? Die bisherige URL wird ungültig und bestehende Abos müssen mit der neuen URL neu eingerichtet werden.',
     caldav_hint: 'Jeder mit dieser URL kann diesen Kalender abonnieren und bearbeiten – kein Login nötig. Über CalDAV-fähige Clients (Apple Kalender, Thunderbird, DAVx5) einbinden.',
     caldav_login_url: 'CalDAV-URL (mit Login):',
-    caldav_login_hint: 'Alternativ im Client ein „CalDAV-Konto" mit dieser Server-URL sowie deinem Benutzernamen und Passwort hinzufügen – dann werden alle deine veröffentlichten Kalender gefunden.',
+    caldav_login_hint: 'Alternativ im Client ein „CalDAV-Konto" mit dieser Server-URL sowie deinem Benutzernamen und App-Passwort hinzufügen – dann werden alle deine veröffentlichten Kalender gefunden.',
+    app_pw_title: 'App-Passwörter (CalDAV)',
+    app_pw_desc: 'Eigene Passwörter für CalDAV-Clients. Bei aktivem 2FA nötig, da Apps keinen 2FA-Code eingeben können. Jederzeit widerrufbar.',
+    app_pw_label_ph: 'Name (z.B. iPhone)',
+    app_pw_create: 'Erstellen',
+    app_pw_new_label: 'Neues App-Passwort (nur jetzt sichtbar):',
+    app_pw_last_used: 'zuletzt',
+    app_pw_never_used: 'noch nie genutzt',
+    app_pw_revoke: 'Widerrufen',
+    app_pw_none: 'Noch keine App-Passwörter.',
+    app_pw_copied: 'App-Passwort kopiert',
+    app_pw_revoke_confirm: 'Dieses App-Passwort widerrufen? Clients, die es nutzen, verlieren den Zugriff.',
     share: 'Teilen',
     import: 'Importieren',
     export: 'Exportieren',
@@ -428,7 +439,18 @@ const translations = {
     caldav_rotate_confirm: 'Generate a new token? The current URL will stop working and existing subscriptions must be re-added with the new URL.',
     caldav_hint: 'Anyone with this URL can subscribe to and edit this calendar — no login required. Add it in a CalDAV-capable client (Apple Calendar, Thunderbird, DAVx5).',
     caldav_login_url: 'CalDAV URL (with login):',
-    caldav_login_hint: 'Alternatively add a "CalDAV account" in your client using this server URL plus your username and password — it will discover all your published calendars.',
+    caldav_login_hint: 'Alternatively add a "CalDAV account" in your client using this server URL plus your username and app password — it will discover all your published calendars.',
+    app_pw_title: 'App passwords (CalDAV)',
+    app_pw_desc: "Dedicated passwords for CalDAV clients. Required when 2FA is on, since apps can't enter a 2FA code. Revocable anytime.",
+    app_pw_label_ph: 'Name (e.g. iPhone)',
+    app_pw_create: 'Create',
+    app_pw_new_label: 'New app password (shown only now):',
+    app_pw_last_used: 'last used',
+    app_pw_never_used: 'never used',
+    app_pw_revoke: 'Revoke',
+    app_pw_none: 'No app passwords yet.',
+    app_pw_copied: 'App password copied',
+    app_pw_revoke_confirm: 'Revoke this app password? Clients using it will lose access.',
     share: 'Share',
     import: 'Import',
     export: 'Export',

frontend/js/version.js

@@ -1,2 +1,2 @@
 // Increment APP_VERSION with every code change
-export const APP_VERSION = 'v67';
+export const APP_VERSION = 'v68';