feat: add personal ics feeds for assigned tasks

app/models.py

@@ -1,5 +1,6 @@
 from __future__ import annotations
 
+import secrets
 from datetime import UTC, date, datetime, timedelta
 
 from flask_login import UserMixin
@@ -24,6 +25,7 @@ class User(UserMixin, TimestampMixin, db.Model):
     password_hash = db.Column(db.String(255), nullable=False)
     is_admin = db.Column(db.Boolean, nullable=False, default=False)
     avatar_path = db.Column(db.String(255), nullable=True)
+    calendar_feed_token = db.Column(db.String(255), nullable=True, unique=True, index=True)
     notification_task_due_enabled = db.Column(db.Boolean, nullable=False, default=True)
     notification_monthly_winner_enabled = db.Column(db.Boolean, nullable=False, default=True)
 
@@ -60,6 +62,11 @@ class User(UserMixin, TimestampMixin, db.Model):
     def check_password(self, password: str) -> bool:
         return check_password_hash(self.password_hash, password)
 
+    def ensure_calendar_feed_token(self) -> str:
+        if not self.calendar_feed_token:
+            self.calendar_feed_token = secrets.token_urlsafe(32)
+        return self.calendar_feed_token
+
     @property
     def display_avatar(self) -> str:
         return self.avatar_path or "images/avatars/default.svg"