diff --git a/radicale/auth/__init__.py b/radicale/auth/__init__.py
index 566b99657..4bb4b33df 100644
--- a/radicale/auth/__init__.py
+++ b/radicale/auth/__init__.py
@@ -29,7 +29,7 @@
 
 """
 
-from typing import Sequence, Set, Tuple, Union
+from typing import Sequence, Set, Tuple, Union, final
 
 from radicale import config, types, utils
 from radicale.log import logger
@@ -50,7 +50,6 @@ def load(configuration: "config.Configuration") -> "BaseAuth":
     return utils.load_plugin(INTERNAL_TYPES, "auth", "Auth", BaseAuth,
                              configuration)
 
-
 class BaseAuth:
 
     _ldap_groups: Set[str] = set([])
@@ -102,6 +101,7 @@ def _login(self, login: str, password: str) -> str:
 
         raise NotImplementedError
 
+    @final
     def login(self, login: str, password: str) -> str:
         if self._lc_username:
             login = login.lower()
diff --git a/radicale/auth/dovecot.py b/radicale/auth/dovecot.py
index 34180eb52..ce2353a0b 100644
--- a/radicale/auth/dovecot.py
+++ b/radicale/auth/dovecot.py
@@ -32,7 +32,7 @@ def __init__(self, configuration):
         self.timeout = 5
         self.request_id_gen = itertools.count(1)
 
-    def login(self, login, password):
+    def _login(self, login, password):
         """Validate credentials.
 
         Check if the ``login``/``password`` pair is valid according to Dovecot.
diff --git a/radicale/auth/ldap.py b/radicale/auth/ldap.py
index 2db88c954..cb3858dcd 100644
--- a/radicale/auth/ldap.py
+++ b/radicale/auth/ldap.py
@@ -202,7 +202,7 @@ def _login3(self, login: str, password: str) -> str:
             pass
         return ""
 
-    def login(self, login: str, password: str) -> str:
+    def _login(self, login: str, password: str) -> str:
         """Validate credentials.
         In first step we make a connection to the ldap server with the ldap_reader_dn credential.
         In next step the DN of the user to authenticate will be searched.
diff --git a/radicale/tests/custom/auth.py b/radicale/tests/custom/auth.py
index 490ec3139..2927ee4d6 100644
--- a/radicale/tests/custom/auth.py
+++ b/radicale/tests/custom/auth.py
@@ -29,7 +29,7 @@
 
 class Auth(auth.BaseAuth):
 
-    def login(self, login: str, password: str) -> str:
+    def _login(self, login: str, password: str) -> str:
         if login == "tmp":
             return login
         return ""