use urljoin to create fallback country data URL (#50585)

src/authentic2_auth_fedict/fields.py

@@ -16,6 +16,7 @@
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
 import time
+from urllib.parse import urljoin
 
 from django import forms
 from django.conf import settings
@@ -112,7 +113,7 @@ class CountryWidget(forms.Select):
             country_url = settings.IMIO_COUNTRY_URL
         else:
             passerelle_url = list(settings.KNOWN_SERVICES['passerelle'].values())[0]['url']
-            country_url = '%s/csvdatasource/pays/data' % passerelle_url
+            country_url = urljoin(passerelle_url, '/csvdatasource/pays/data')
         try:
             self.choices = [(x['id'], x['text']) for x in requests.get(country_url).json()['data']]
         except ValueError: