Clean a CAS-returned username

cas.eleves.ens.fr allows users such as '  FooBAr ' or 'foobar' in
indifferently

bocal/settings_base.py

@@ -87,7 +87,7 @@ AUTH_PASSWORD_VALIDATORS = [
 
 AUTHENTICATION_BACKENDS = [
     'django.contrib.auth.backends.ModelBackend',
-    'django_cas_ng.backends.CASBackend',
+    'mainsite.cas_backend.BOcalCASBackend',
 ]
 
 CAS_ADMIN_PREFIX = '/yaes5eiS'  # we don't want CAS to take over /admin auth

mainsite/cas_backend.py

@@ -0,0 +1,7 @@
+from django_cas_ng.backends import CASBackend
+
+
+class BOcalCASBackend(CASBackend):
+    # Partly from Robin Champenois's "ExperiENS". Thanks!
+    def clean_username(self, username):
+        return username.lower().strip()