Log mTLS auth failures

mailman_api/tls_auth.py

@@ -61,6 +61,8 @@ def tls_auth(fn):
         for acl_path, acl_cn_rx in current_app.tls_auth_acls:
             if request.path.startswith(acl_path) and _regexp_match(acl_cn_rx, cn):
                 return fn(*args, **kwargs)
+        current_app.logger.error(
+            'unauthenticated mTLS request, path=%s peer=%s', request.path, cn)
         abort(403)
     return _tls_auth_wrapper