fix old subscribers group attribution

Si un utilisateur faisait sa première cotisation alors qu'il avait déjà un compte AE (par exemple, en effectuant un achat sur l'eboutic avant sa cotisation), alors il pouvait se retrouver hors du groupe Anciens cotisants.

subscription/views.py

@@ -14,6 +14,7 @@
 #
 
 from django.conf import settings
+from django.contrib.auth.forms import PasswordResetForm
 from django.contrib.auth.mixins import PermissionRequiredMixin
 from django.core.exceptions import PermissionDenied
 from django.urls import reverse, reverse_lazy
@@ -65,11 +66,23 @@ class CreateSubscriptionExistingUserFragment(CreateSubscriptionFragment):
 
 
 class CreateSubscriptionNewUserFragment(CreateSubscriptionFragment):
-    """Create a subscription for a user who already exists."""
+    """Create a subscription for a user who doesn't exist yet."""
 
     form_class = SubscriptionNewUserForm
     extra_context = {"post_url": reverse_lazy("subscription:fragment-new-user")}
 
+    def form_valid(self, form):
+        res = super().form_valid(form)
+        reset_form = PasswordResetForm({"email": form.cleaned_data["email"]})
+        if reset_form.is_valid():
+            reset_form.save(
+                use_https=True,
+                email_template_name="core/new_user_email.jinja",
+                subject_template_name="core/new_user_email_subject.jinja",
+                from_email="ae@utbm.fr",
+            )
+        return res
+
 
 class SubscriptionCreatedFragment(PermissionRequiredMixin, DetailView):
     template_name = "subscription/fragments/creation_success.jinja"