Add user post deletion

Users can delete their posts as long as they don't clear their cookies,
and as long as server-side user sessions are persistent.

Signed-off-by: Alek Ratzloff <alekratz@gmail.com>

board/utils.py

@@ -1,6 +1,9 @@
 from typing import Optional, TYPE_CHECKING
 from django.utils import timezone
+from django.conf import settings
 import ipaddress
+import random
+import string
 
 from board.models import Ban, RangeBan
 
@@ -45,3 +48,11 @@ def is_banned(ip: str, board: Optional["Board"]) -> bool:
         return bool(active)
     else:
         return False
+
+
+def generate_user_token() -> str:
+    """
+    Generates a non-secure user token.
+    User tokens need not be secure so this is a simple implementation.
+    """
+    return "".join(random.choices(string.ascii_letters, k=settings.USER_TOKEN_LENGTH))