Make invitation link duration configurable

greg/utils.py

 import re
 import typing
 from datetime import date, datetime, timedelta
+from django.conf import settings
 from django.utils import timezone
 
 from greg.models import Identity
@@ -114,7 +115,7 @@ def date_to_datetime_midnight(in_date: typing.Union[date, str]) -> datetime:
 
 
 def get_default_invitation_expire_date_from_now():
-    return timezone.now() + timedelta(days=30)
+    return timezone.now() + timedelta(days=settings.INVITATION_DURATION)
 
 
 def is_identity_duplicate(identity_type: Identity.IdentityType, value: str) -> bool:

gregsite/settings/base.py

@@ -295,6 +295,8 @@ BASE_URL = "https://example.org"
 
 FEIDE_SOURCE = "feide"
 
+# The default duration for a new invitation link, in days
+INVITATION_DURATION = 30
 
 # Used by the OU import from orgreg to distinguish the OuIdentifiers from others
 ORGREG_SOURCE = "orgreg"