diff --git a/authens/backends.py b/authens/backends.py
index ebea500..e5719e3 100644
--- a/authens/backends.py
+++ b/authens/backends.py
@@ -52,14 +52,18 @@ class ENSCASBackend:
 
     def authenticate(self, request, ticket=None):
         cas_client = get_cas_client(request)
-        uid, attributes, _ = cas_client.verify_ticket(ticket)
+        cas_login, attributes, _ = cas_client.verify_ticket(ticket)
 
-        if not uid:
+        if cas_login is None:
             # Authentication failed
             return None
 
+        cas_login = self.clean_cas_login(cas_login)
         year = get_entrance_year(attributes)
-        return self._get_or_create(uid, year)
+        return self._get_or_create(cas_login, year)
+
+    def clean_cas_login(self, cas_login):
+        return cas_login.strip().lower()
 
     def get_free_username(self, cas_login):
         """Find an available username for a new user.