diff --git a/radicale/auth/oauth2.py b/radicale/auth/oauth2.py
index 4efde374..cfa5dbe5 100644
--- a/radicale/auth/oauth2.py
+++ b/radicale/auth/oauth2.py
@@ -1,3 +1,25 @@
+# This file is part of Radicale Server - Calendar Server
+#
+# Original from https://gitlab.mim-libre.fr/alphabet/radicale_oauth/
+# Copyright © 2021-2022 Bruno Boiget
+# Copyright © 2022-2022 Daniel Dehennin
+#
+# Since migration into upstream
+# Copyright © 2025-2025 Peter Bieringer <pb@bieringer.de>
+#
+# This library is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This library is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with Radicale.  If not, see <http://www.gnu.org/licenses/>.
+
 """
 Authentication backend that checks credentials against an oauth2 server auth endpoint
 """