Make username generation hackable

authens/backends.py

@@ -30,21 +30,6 @@ def get_entrance_year(attributes):
         return 2000 + year
 
 
-def find_available_username(clipper_uid):
-    """Find an available username 'close' to a clipper uid."""
-
-    taken = UserModel.objects.filter(username__startswith=clipper_uid).values_list(
-        "username", flat=True
-    )
-    if clipper_uid not in taken:
-        return clipper_uid
-    else:
-        i = 2
-        while clipper_uid + str(i) in taken:
-            i += 1
-        return clipper_uid + str(i)
-
-
 class ENSCASBackend:
     """ENSAuth authentication backend.
 
@@ -72,6 +57,31 @@ class ENSCASBackend:
         year = get_entrance_year(attributes)
         return self._get_or_create(uid, year)
 
+    def find_available_username(self, clipper_uid):
+        """Find an available username for the new user.
+
+        If you override this method, make sure it returns a username that is not taken
+        by any existing user.
+        This method will be called from within an atomic database transation (don't
+        worry about data races).
+        """
+
+        taken = UserModel.objects.values_list("username", flat=True)
+
+        # This should handle most cases and produce a nice username.
+        prefered = [clipper_uid, "cas_" + clipper_uid]
+        pref_taken = taken.filter(username__in=prefered)
+        for name in prefered:
+            if name not in pref_taken:
+                return name
+
+        # Worst case: generate a username of the form clipper_uid + int
+        taken = taken.filter(username__startswith=clipper_uid)
+        i = 2
+        while clipper_uid + str(i) in taken:
+            i += 1
+        return clipper_uid + str(i)
+
     def _get_or_create(self, uid, entrance_year):
         with transaction.atomic():
             try:
@@ -83,7 +93,7 @@ class ENSCASBackend:
                 user = None
 
             if user is None:
-                username = find_available_username(uid)
+                username = self.find_available_username(uid)
                 user = UserModel.objects.create_user(username=username)
                 Clipper.objects.create(user=user, entrance_year=entrance_year, uid=uid)
         return user