Only allow letters, numbers, dots and dashes for giftcard codes

src/pretix/base/models/giftcards.py

@@ -1,6 +1,7 @@
 from decimal import Decimal
 
 from django.conf import settings
+from django.core.validators import RegexValidator
 from django.db import models
 from django.db.models import Sum
 from django.utils.crypto import get_random_string
@@ -50,6 +51,12 @@ class GiftCard(LoggedModel):
         max_length=190,
         db_index=True,
         verbose_name=_('Gift card code'),
+        validators=[
+            RegexValidator(
+                regex="^[a-zA-Z0-9][a-zA-Z0-9.-]+$",
+                message=_("The giftcard code may only contain letters, numbers, dots and dashes."),
+            )
+        ],
     )
     testmode = models.BooleanField(
         verbose_name=_('Test mode card'),